Method, device, and system for transmitting signals in unlicensed band

ABSTRACT

A method, a device, and a system for transmitting a downlink signal is provided. The method includes monitoring a first common control channel indicating a downlink (DL) interval of subframe (SF) #(n−1) and SF #n, monitoring a second common control channel indicating a DL interval of SF #n and SF #(n+1), and performing a DL reception process in the SF #n based on a detection result of the first common control channel and a detection result of second common control channel. The DL interval represents occupied OFDM symbols in a DL subframe.

TECHNICAL FIELD

The present invention relates to a wireless communication system.Specifically, the present invention relates to a method, device, andsystem for performing a signal in an unlicensed band.

BACKGROUND ART

In recent years, with an explosive increase of mobile traffic due to thespread of smart devices, it has been difficult to cope with data usagewhich increases for providing a cellular communication service only by aconventional licensed frequency spectrum or LTE-licensed frequency band.

In such a situation, a scheme that uses an unlicensed (alternatively,unauthorized, non-licensed, or license unnecessary) frequency spectrumor LTE-Unlicensed frequency band (e.g., 2.4 GHz band, 5 GHz band, or thelike) for providing the cellular communication service has been devisedas a solution for a spectrum shortage problem.

However, unlike the licensed band in which a communication serviceprovider secures an exclusive frequency use right through a proceduresuch as auction, or the like, in the unlicensed band, multiplecommunication facilities can be used simultaneously without limit whenonly a predetermined level of adjacent band protection regulation isobserved. As a result, when the unlicensed band is used in the cellularcommunication service, it is difficult to guarantee communicationquality at a level provided in the licensed band and an interferenceproblem with a conventional wireless communication device (e.g.,wireless LAN device) using the unlicensed band may occur.

Therefore, a research into a coexistence scheme with the conventionalunlicensed band device and a scheme for efficiently sharing a radiochannel needs to be preferentially made in order to settle an LTEtechnology in the unlicensed band. That is, a robust coexistencemechanism (RCM) needs to be developed in order to prevent a device usingthe LTE technology in the unlicensed band from influencing theconventional unlicensed band device.

DISCLOSURE Technical Problem

The present invention has been made in an effort to provide a method forefficiently transmitting/receiving a signal in a wireless communicationsystem, in particular, a cellular wireless communication system and anapparatus therefor. Further, the present invention has been made in aneffort to provide a method for efficiently transmitting/receiving asignal in a specific frequency band (e.g., unlicensed band) and anapparatus therefor.

Technical objects desired to be achieved in the present invention arenot limited to the aforementioned objects, and other technical objectsnot described above will be apparently understood by those skilled inthe art from the following disclosure.

Technical Solution

According to an embodiment of the present invention, a method for a userequipment to receive a downlink signal in a cellular communicationsystem includes monitoring a first common control channel indicating adownlink (DL) interval of subframe (SF) #(n−1) and SF #n; monitoring asecond common control channel indicating a DL interval of SF #n and SF#(n+1); and performing a DL reception process in the SF #n based on adetection result of the first common control channel and a detectionresult of the second common control channel, wherein only a detectionprocess for a first physical channel/signal is allowed in the DLreception process in SF #n when a detection of the first common controlchannel fails, a detection of the second common control channel issuccessful, and the DL interval of SF #n indicated by the second commoncontrol channel is a part a total OFDM symbols of SF #n, wherein thefirst physical channel/signal includes a Discovery Reference Signal(DRS). The DL interval may represent occupied OFDM symbols in a DLsubframe.

According to another embodiment of the present invention, a userequipment used in a cellular wireless communication system includes: awireless communication module; and a processor, wherein the processor isconfigured to monitor a first common control channel indicating adownlink (DL) interval of subframe (SF) #(n−1) and SF #n; monitors asecond common control channel indicating a DL interval of SF #n and SF#(n+1); and performs a DL reception process in the SF #n based on adetection result of the first common control channel and a detectionresult of second common control channel, wherein only a detectionprocess for a first physical channel/signal is allowed in the DLreception process in SF #n when a detection of the first common controlchannel fails, a detection of the second common control channel issuccessful, and the DL interval of SF #n indicated by the second commoncontrol channel is a part of a total OFDM symbols of SF #n, wherein thefirst physical channel/signal includes a Discovery Reference Signal(DRS). The DL interval may represent occupied OFDM symbols in a DLsubframe.

A reception process for a second physical channel/signal may be omittedin SF #n when the detection of the first common control channel fails,the detection of the second common control channel is successful, andthe DL interval of SF #n is a part of SF #n, wherein the second physicalchannel/signal may not include the DRS.

The second physical channel/signal may include a Physical DownlinkControl Channel (PDCCH), an Enhanced PDCCH (EPDCCH), and a PhysicalDownlink Shared Channel (PDSCH) for downlink transmission.

The first common control channel may be monitored in SF #(n−1), and thesecond common control channel may be monitored in SF #n.

SF #n may be included in a time window expecting DRS reception.

The time window expecting the DRS reception may include a DRSMeasurement Timing configuration (DMTC).

The DMTC may be configured in a cell of an unlicensed band.

The first and second common control channels may include a PhysicalDownlink Control Channel (PDCCH) scrambled with a Cyclic RedundancyCheck (CRC) by a Common Control Radio Network Temporary Identifier(CC-RNTI).

Advantageous Effects

According to exemplary embodiments of the present invention, providedare a method for efficiently transmitting/receiving a signal in awireless communication system, in particular, a cellular wirelesscommunication system and an apparatus therefor. Further, provided are amethod for efficiently transmitting/receiving a signal in a specificfrequency band (e.g., unlicensed band) and an apparatus therefor.

Effects to be acquired in the present invention are not limited to theaforementioned effects, and other effects not described above will beapparently understood by those skilled in the art from the followingdisclosure.

DESCRIPTION OF DRAWINS

In order to help understand the present invention, the accompanyingdrawings which are included as a part of the Detailed Descriptionprovide embodiments of the present invention and describe the technicalmatters of the present invention together with the Detailed Description.

FIG. 1 illustrates physical channels used in a 3rd generationpartnership project (3GPP) system and a general signal transmittingmethod using the physical channels.

FIG. 2 illustrates one example of a radio frame structure used in awireless communication system.

FIG. 3 illustrates one example of a downlink (DL)/uplink (UL) slotstructure in the wireless communication system.

FIG. 4 illustrates a structure of a downlink subframe (SF).

FIG. 5 illustrates a structure of an uplink subframe.

FIG. 6 is a diagram for describing single carrier communication andmulti-carrier communication.

FIG. 7 illustrates an example in which a cross carrier schedulingtechnique is applied.

FIG. 8 illustrates Discovery Reference Signal (DRS) transmission.

FIGS. 9 to 11 illustrate the structure of a reference signal used asDRS.

FIG. 12 illustrates a Licensed Assisted Access (LAA) serviceenvironment.

FIG. 13 illustrates a deployment scenario of a user equipment and a basestation in an LAA service environment.

FIG. 14 illustrates a conventional communication scheme operating in anunlicensed band.

FIGS. 15 to 16 illustrate a Listen-Before-Talk (LBT) procedure for DLtransmission.

FIG. 17 illustrates DL transmission in unlicensed band.

FIG. 18 illustrates DRS transmission in unlicensed band.

FIG. 19 illustrates a parameter for LAA DRS transmission and a DRStransmission method based on LBT.

FIGS. 20 and 21 illustrate LAA DRS+PDSCH simultaneous transmission inDMTC.

FIG. 22 illustrates an existing Secondary Synchronization Signal (SSS).

FIG. 23 illustrates a downlink receiving process according to anembodiment of the present invention.

FIG. 24 illustrates a configuration of a user equipment and a basestation according to an embodiment of the present invention.

MODE FOR CARRYING OUT THE INVENTION

Terms used in the specification adopt general terms which are currentlywidely used as possible by considering functions in the presentinvention, but the terms may be changed depending on an intention ofthose skilled in the art, customs, and emergence of new technology.Further, in a specific case, there is a term arbitrarily selected by anapplicant and in this case, a meaning thereof will be described in acorresponding description part of the invention. Accordingly, it intendsto be revealed that a term used in the specification should be analyzedbased on not just a name of the term but a substantial meaning of theterm and contents throughout the specification.

Throughout this specification and the claims that follow, when it isdescribed that an element is “coupled” to another element, the elementmay be “directly coupled” to the other element or “electrically coupled”to the other element through a third element. Further, unless explicitlydescribed to the contrary, the word “comprise” and variations such as“comprises” or “comprising”, will be understood to imply the inclusionof stated elements but not the exclusion of any other elements.Moreover, limitations such as “equal to or more than” or “equal to orless than” based on a specific threshold may be appropriatelysubstituted with “more than” or “less than”, respectively in someexemplary embodiments.

The following technology may be used in various wireless access systems,such as code division multiple access (CDMA), frequency divisionmultiple access (FDMA), time division multiple access (TDMA), orthogonalfrequency division multiple access (OFDMA), single carrier-TDMA(SC-FDMA), and the like. The CDMA may be implemented by a radiotechnology such as universal terrestrial radio access (UTRA) orCDMA2000. The TDMA may be implemented by a radio technology such asglobal system for mobile communications (GSM)/general packet radioservice (GPRS)/enhanced data rates for GSM evolution (EDGE). The OFDMAmay be implemented by a radio technology such as IEEE 802.11(Wi-Fi),IEEE 802.16(WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), and the like.The UTRA is a part of a universal mobile telecommunication system(UMTS). 3^(rd) generation partnership project (3GPP) long term evolution(LTE) is a part of an evolved UMTS (E-UMTS) using evolved-UMTSterrestrial radio access (E-UTRA) and LTE-advanced (A) is an evolvedversion of the 3GPP LTE. 3GPP LTE/LTE-A is primarily described for cleardescription, but technical spirit of the present invention is notlimited thereto.

FIG. 1 illustrates physical channels used in a 3GPP system and a generalsignal transmitting method using the physical channels. An userequipment receives information from a base station through downlink (DL)and the user equipment transmits information through uplink (UL) to thebase station. The information transmitted/received between the basestation and the user equipment includes data and various controlinformation and various physical channels exist according to atype/purpose of the information transmitted/received between the basestation and the user equipment.

When a power of the user equipment is turned on or the user equipmentnewly enters a cell, the user equipment performs an initial cell searchoperation including synchronization with the base station, and the like(S301). To this end, the user equipment receives a primarysynchronization channel (P-SCH) and a secondary synchronization channel(S-SCH) from the base station to synchronize with the base station andobtain information including a cell ID, and the like. Thereafter, theuser equipment receives a physical broadcast channel from the basestation to obtain intra-cell broadcast information. The user equipmentreceives a downlink reference signal (DL RS) in an initial cell searchstep to verify a downlink channel state.

The user equipment that completes initial cell search receives aphysical downlink control channel (PDCCH) and a physical downlink sharedchannel (PDSCH) depending on information loaded on the PDCCH to obtainmore detailed system information (S302).

When there is no radio resource for initially accessing the base stationor signal transmission, the user equipment may perform a random accessprocedure (RACH procedure) to the base station (S303 to S306). To thisend, the user equipment may transmit a preamble through a physicalrandom access channel (PRACH) (S303) and receive a response message tothe preamble through the PDCCH and the PDSCH corresponding thereto(S304). In the case of a contention based RACH, a contention resolutionprocedure may be additionally performed.

Thereafter, the user equipment may receive the PDCCH/PDSCH (S307) andtransmit a physical uplink shared channel (PUSCH)/physical uplinkcontrol channel (PUCCH) (S308) as a general procedure. The userequipment receives downlink control information (DCI) through the PDCCH.The DCI includes control information such as resource allocationinformation to the user equipment and a format varies depending on a usepurpose. The control information which the user equipment transmits tothe base station is designated as uplink control information (UCI). TheUCI includes an acknowledgement/negative acknowledgement (ACK/NACK), achannel quality indicator (CQI), a precoding matrix index (PMI), a rankindicator (RI), and the like. The UCI may be transmitted through thePUSCH and/or PUCCH.

FIG. 2 illustrates one example of a radio frame structure used in awireless communication system. FIG. 2A illustrates a frame structure forfrequency division duplex (FDD) and FIG. 2B illustrates a framestructure for time division duplex (TDD).

Referring to FIG. 2, a radio frame may have a length of 10 ms (307200Ts) and be constituted by 10 subframes (SFs). Ts represents a samplingtime and is expressed as Ts=1/(2048*15 kHz). Each subframe may have alength of 1 ms and be constituted by 2 slots. Each slot has a length of0.5 ms. A time for transmitting one subframe is defined as atransmission time interval (TTI). A time resource may be distinguishedby radio frame numbers/indexes, subframe numbers/indexes #0 to #9, andslot numbers/indexes #0 to #19.

The radio frame may be configured differently according to a duplexmode. In an FDD mode, downlink transmission and uplink transmission aredistinguished by a frequency and the radio frame includes only one of adownlink subframe and an uplink subframe with respect to a specificfrequency band. In a TDD mode, the downlink transmission and the uplinktransmission are distinguished by a time and the radio frame includesboth the downlink subframe and the uplink subframe with respect to aspecific frequency band. The TDD radio frame further includes specialsubframes for downlink and uplink switching. The special subframeincludes a Downlink Pilot Time Slot (DwPTS), a guard period (GP), and anUplink Pilot Time Slot (UpPTS).

FIG. 3 illustrates a structure of a downlink/uplink slot.

Referring to FIG. 3, the slot includes a plurality of orthogonalfrequency divisional multiplexing (OFDM) symbols in a time domain and aplurality of resource blocks (RBs) in a frequency domain. The OFDMsymbol also means one symbol period. The OFDM symbol may be called anOFDMA symbol, a single carrier frequency division multiple access(SC-FDMA) symbol, or the like according to a multi-access scheme. Thenumber of OFDM symbols included in one slot may be variously modifiedaccording to the length of a cyclic prefix (CP). For example, in thecase of a normal CP, one slot includes 7 OFDM symbols and in the case ofan extended CP, one slot includes 6 OFDM symbols. The RB is defined asN^(DL/UL) _(symb) (e.g., 7) continuous OFDM symbols in the time domainand N^(RB) _(sc) (e.g., 12) continuous subcarriersin the frequencydomain A resource constituted by one OFDM symbol and one subcarrier isreferred to as a resource element (RE) or a tone. One RB is constitutedby N^(DL/UL) _(symb)*N^(RB) _(sc) resource elements.

The resource of the slot may be expressed as a resource grid constitutedby N^(DL/UL) _(RB)*Nhu RB_(sc) subcarriers and N^(DL/UL) _(symb) OFDMsymbols. Each RE in the resource grid is uniquely defined by an indexpair (k, 1) for each slot. k represents an index given with 0 toN^(DLUL) _(RB)*N^(RB) _(sc)-1 in the frequency domain and 1 representsan index given with 0 to N^(DL/UL) _(symb)-1 in the time domain. Herein,N^(DL) _(RB) represents the number of resource blocks (RBs) in thedownlink slot and N^(UL) _(RB) represents the number of RBs in the ULslot. N^(DL) _(RB) and N^(UL) _(RB) depend on a DL transmissionbandwidth and a UL transmission bandwidth, respectively. N^(DL) _(symb)represents the number of symbols in the downlink slot and N^(UL) _(symb)represents the number of symbols in the UL slot. N^(RB) _(sc) representsthe number of subcarriers constituting one RB. One resource grid isprovided per antenna port.

FIG. 4 illustrates a structure of a downlink subframe.

Referring to FIG. 4, the subframe may be constituted by 14 OFDM symbols.First 1 to 3 (alternatively, 2 to 4) OFDM symbols are used as a controlregion and the remaining 13 to 11 (alternatively, 12 to 10) OFDM symbolsare used as a data region according to subframe setting. R1 to R4represent reference signals for antenna ports 0 to 3. Control channelsallocated to the control region include a physical control formatindicator channel (PCFICH), a physical hybrid-ARQ indicator channel(PHICH), a physical downlink control channel (PDCCH), and the like. Datachannels allocated to the data region include the PDSCH, and the like.When an enhanced PDCCH (EPDCCH) is set, the PDSCH and the EPDCCH aremultiplexed by frequency division multiplexing (FDM) in the data region.

The PDCCH as the physical downlink control channel is allocated to firstn OFDM symbols of the subframe. n as an integer of 1(alternatively, 2)or more is indicated by the PCFICH. The PDCCH announces informationassociated with resource allocation of a paging channel (PCH) and adownlink-shared channel (DL-SCH) as transmission channels, an uplinkscheduling grant, HARQ information, and the like to each user equipmentor user equipment group. Data (that is, transport block) of the PCH andthe DL-SCH are transmitted through the PDSCH. Each of the base stationand the user equipment generally transmit and receive data through thePDSCH except for specific control information or specific service data.

Information indicating to which user equipment (one or a plurality ofuser equipments) the data of the PDSCH is transmitted, informationindicating how the user equipments receive and decode the PDSCH data,and the like are transmitted while being included in the PDCCH/EPDCCH.For example, it is assumed that the PDCCH/EPDCCH is CRC-masked with aradio network temporary identity (RNTI) called “A” and informationregarding data transmitted by using a radio resource (e.g., frequencylocation) called “B” and a DCI format called “C”, that is, transmissionformat information (e.g., transport block size, modulation scheme,coding information, and the like) is transmitted through a specificsubframe. In this case, a user equipment in the cell monitors thePDCCH/EPDCCH by using the RNTI information thereof and when one or moreuser equipments having the “A” RNTI are provided, the user equipmentsreceive the PDCCH/EPDCCH and receive the PDSCH indicated by “B” and “C”through information on the received PDCCH/EPDCCH.

FIG. 5 illustrates a structure of an uplink subframe.

Referring to FIG. 5, the subframe may be divided into the control regionand the data region in the frequency domain. The PUCCH is allocated tothe control region and carries the UCI. The PUSCH is allocated to thedata region and carries user data.

The PUCCH may be used to transmit the following control information.

-   -   Scheduling Request (SR): Information used to request a UL-SCH        resource. The SR is transmitted by using an on-off keying (OOK)        scheme.    -   HARQ-ACK: Response to the PDCCH and/or response to a downlink        data packet (e.g., codeword) on the PDSCH. The codeword is an        encoded format of the transport block. The HARQ-ACK indicates        whether the PDCCH or PDSCH is successfully received. The        HARQ-ACK response includes a positive ACK (simply, ACK), a        negative ACK (NACK), discontinuous transmission (DTX), or the        NACK/DTX. The DTX represents a case in which the user equipment        misses the PDCCH (alternatively, semi-persistent scheduling        (SPS) PDSCH) and the NACK/DTX means the NACK or DTX. The        HARQ-ACK is mixedly used with the HARQ-ACK/NACK and the        ACK/NACK.    -   Channel State Information (CSI): Feed-back information regarding        the downlink channel. Multiple input multiple output (MIMO)        related feed-back information includes the RI and the PMI.

Table 1 shows the relationship between a PUCCH format and the UCI.

TABLE 1 PUCCH Format Uplink control information (UCI) Format 1Scheduling request (SR) (non-modulated waveform) Format 1a 1-bit HARQACK/NACK (SR existence/non-existence) Format 1b 2-bit HARQ ACK/NACK (SRexistence/non-existence) Format 2 CSI (20 coded bits) Format 2 CSI and 1or 2-bit HARQ ACK/NACK (20 bits) (corresponding to only extended CP)Format 2a CSI and 1-bit HARQ ACK/NACK (20 + 1 coded bits) Format 2b CSIand 2-bit HARQ ACK/NACK (20 + 2 coded bits) Format 3 HARQ ACK/NACK + SR(48 coded bits) (LTE-A)

Hereinafter, carrier aggregation will be described. The carrieraggregation means a method in which the wireless communication systemuses a plurality of frequency blocks as one large logical frequency bandin order to use a wider frequency band. When a whole system band isextended by the carrier aggregation, a frequency band used forcommunication with each user equipment is defined by a component carrier(CC) unit.

FIG. 6 is a diagram for describing single carrier communication andmulti-carrier communication. FIG. 6A illustrates a subframe structure ofa single carrier and

FIG. 6B illustrates a subframe structure of multi-carriers which arecarrier-aggregated.

Referring to FIG. 6A, in a single carrier system, the base station andthe user equipment perform data communication through one DL band andone UL band corresponding thereto. The DL/UL band is divided into aplurality of orthogonal subcarriers and each frequency band operates atone carrier frequency. In the FDD, the DL and UL bands operate atdifferent carrier frequencies, respectively and in the TDD, the DL andUL bands operate at the same carrier frequency. The carrier frequencymeans a center frequency of the frequency band.

Referring to FIG. 6B, the carrier aggregation is distinguished from anOFDM system that performs DL/UL communication in a base frequency banddivided into a plurality of subcarriers by using one carrier frequency,in that the carrier aggregation performs DL/UL communicationby using aplurality of carrier frequencies. Referring to FIG. 6B, three 20 MHz CCsare gathered in each of the UL and the DL to support a bandwidth of 60MHz. The CCs may be adjacent to each other or non-adjacent to each otherin the frequency domain. For convenience, FIG. 6B illustrates a case inwhich a bandwidth of a UL CC and a bandwidth of a DL CC are the same aseach other and symmetric to each other, but the bandwidths of therespective CCs may be independently decided. Further, asymmetric carrieraggregation in which the number of UL CCs and the number of DL CCs aredifferent from each other is also available. The DL/UL CC(s) areindependently allocated/configured for each user equipment and the DL/ULCC(s) allocated/configured to the user equipment are designated asserving UL/DL CC(s) of the corresponding user equipment.

The base station may activate some or all of serving CCs of the userequipment or deactivate some CCs. When the base station allocates theCC(s) to the user equipment, if the CC allocation to the user equipmentis wholly reconfigured or if the user equipment does not hand over, atleast one specific CC among the CC(s) configured with respect to thecorresponding user equipment is not deactivated. A specific CC which isalways activated is referred to as a primary CC (PCC) and a CC which thebase station may arbitrarily activate/deactivate is referred to as asecondary CC (SCC). The PCC and the SCC may be distinguished based onthe control information. For example, specific control information maybe set to be transmitted/received only through a specific CC and thespecific CC may be referred to as the PCC and remaining CC(s) may bereferred to as SCC(s). The PUCCH is transmitted only on the PCC.

In 3GPP, a concept of the cell is used in order to manage the radioresource. The cell is defined as a combination of the DL resource andthe UL resource, that is, a combination of the DL CC and the UL CC. Thecell may be configured by the DL resource only or the combination of theDL resource and the UL resource. When the carrier aggregation issupported, a linkage between the carrier frequency of the DL resource(alternatively, DL CC) and the carrier frequency of the UL resource(alternatively, UL CC) may be indicated by system information. Forexample, the combination of the DL resource and the UL resource may beindicated by a system information block type 2 (SIB2) linkage. Thecarrier frequency means a center frequency of each cell or CC. A cellcorresponding to the PCC is referred to as the primary cell (PCell) anda cell corresponding to the SCC is referred to as the secondary cell(SCell). A carrier corresponding to the PCell is a DL PCC in thedownlink and a carrier corresponding to the PCell is a UL PCC in theuplink. Similarly, a carrier corresponding to the SCell is a DL SCC inthe downlink and a carrier corresponding to the SCell is a UL SCC in theuplink. According to a user equipment capability, the serving cell(s)may be constituted by one PCell and 0 or more SCells. For a userequipment which is in an RRC_CONNECTED state, but does not have anyconfiguration for the carrier aggregation or does not support thecarrier aggregation, only one serving cell constituted by only the PCellis present.

FIG. 7 illustrates an example in which cross carrier scheduling isapplied. When the cross carrier scheduling is configured, a controlchannel transmitted through a first CC may schedule a data channeltransmitted through the first CC or a second CC by using a carrierindicator field (CIF). The CIF is included in the DCI. In other words, ascheduling cell is configured, and a DL grant/UL grant transmitted in aPDCCH area of the scheduling cell schedules the PDSCH/PUSCH of ascheduled cell. That is, a search space for a plurality of componentcarriers is present in the PDCCH area of the scheduling cell. The PCellmay be basically the scheduling cell and a specific SCell may bedesignated as the scheduling cell by an upper layer.

In FIG. 7, it is assumed that three DL CCs are aggregated. Herein, DLcomponent carrier #0 is assumed as the DL PCC (alternatively, PCell) andDL component carrier #1 and DL component carrier #2 are assumed as theDL SCC (alternatively, SCell). Further, it is assumed that the DL PCC isset as a PDCCH monitoring CC. When the CIF is disabled, the respectiveDL CCs may transmit only the PDCCH that schedules the PDSCH thereofwithout the CIF according to an LTE PDCCH rule (non-cross carrierscheduling or self-carrier scheduling). On the contrary, when the CIF isenabled by UE-specific (alternatively, UE-group-specific orcell-specific) upper layer signaling, a specific CC (e.g., DL PCC) maytransmit the PDCCH scheduling the PDSCH of DL CC A and the PDCCHscheduling the PDSCH of another CC by using the CIF (cross-carrierscheduling). On the contrary, in another DL CC, the PDCCH is nottransmitted.

Hereinafter, DRS transmission in a licensed band will be described withreference to FIGS. 8 to 11. FIG. 8 illustrates DRS transmission, andFIGS. 9 to 11 illustrate a structure of a reference signal used in DRS.For convenience, DRS in the licensed band is referred to as Rel-12 DRS.DRS supports small cell on/off, and a SCell that is not active for anyuser equipment may be turned off except for DRS periodic transmission.Also, based on the DRS, a user equipment may obtain cell identificationinformation, measure Radio Resource Management (RRM), and obtaindownlink synchronization.

Referring to FIG. 8, a Discovery Measurement Timing Configuration (DMTC)indicates a time window in which a user equipment expects to receiveDRS. The DMTC is fixed at 6 ms. The DMTC period is the transmissionperiod of the DMTC, and may be 40 ms, 80 ms, or 160 ms. The position ofthe DMTC is specified by the DMTC transmission period and the DMTCoffset (in units of subframes), and these information are transmitted tothe user equipment through higher layer signaling (e.g., RRC signaling).DRS transmissions occur at the DRS occasion within the DMTC. The DRSoccasion has a transmission period of 40 ms, 80 ms or 160 ms, and theuser equipment may assume that there is one DRS occasion per DMTCperiod. The DRS occasion includes 1 to 5 consecutive subframes in theFDD radio frame and 2 to 5 consecutive subframes in the TDD radio frame.The length of the DRS occasion is delivered to the user equipment viahigher layer signaling (e.g., RRC signaling). The user equipment mayassume DRS in the DL subframe in the DRS occasion. DRS occasion mayexist anywhere in the DMTC, but the user equipment expects thetransmission interval of DRSs transmitted from the cell to be fixed(i.e., 40 ms, 80 ms, or 160 ms). That is, the position of the DRSoccasion in the DMTC is fixed per cell. The DRS is configured asfollows.

-   -   Cell-specific Reference Signal (CRS) at antenna port 0 (see FIG.        9): It exists in all downlink subframes within the DRS occasion,        and in the DwPTS of all the special subframes. The CRS is        transmitted in the entire band of the subframe.    -   Primary Synchronization Signal (PSS) (see FIG. 10): In the case        of FDD radio frame, it exists in the first subframe in DRS        occasion, or in the second subframe in DRS occasion in the case        of TDD radio frame. The PSS is transmitted in the seventh (or        sixth) OFMDA symbol of the subframe and mapped to six RBs (=72        subcarriers) close to the center frequency.    -   Secondary Synchronization Signal (SSS) (see FIG. 10): It exists        in the first subframe in the DRS occasion. The SSS is        transmitted in the sixth (or fifth) OFMDA symbol of the subframe        and mapped to six RBs (=72 subcarriers) close to the center        frequency.    -   non-zero-power Channel State Information (CSI)-RS (see FIG. 11):        It exists in zero or more subframes in the DRS occasion. The        position of the non-zero-power CSI-RS is variously configured        according to the number of CSI-RS ports and the higher layer        configuration information.

FIG. 8 illustrates a case where the DRS reception time is set to aseparate DMTC for each frequency in a user equipment's situation.Referring to FIG. 8, in the case of frequency F1, a DRS occasion with alength of 2 ms is transmitted every 40 ms, in the case of frequency F2,a DRS occasion with a length of 3 ms is transmitted every 80 ms, and inthe case of frequency F3, a DRS occasion with a length of 4 ms istransmitted every 80 ms. The user equipment may know the startingposition of the DRS occasion in the DMTC from the subframe including theSSS. Here, the frequencies F1 to F3 may be replaced with correspondingcells, respectively.

Embodiment: DRS Transmission Scheme in Unlicensed Band

FIG. 12 illustrates a Licensed Assisted Access (LAA) serviceenvironment.

Referring to FIG. 12, a service environment may be provided to a user,in the service environment, an LTE technology (11) in a conventionallicensed band and LTE-unlicensed (LTE-U) or LAA which is an LTEtechnology (12) in an unlicensed band, which has been actively discussedmay be connected to each other. For example, the LTE technology (11) inthe licensed band and the LTE technology (12) in the unlicensed band inthe LAA environment may be integrated by using a technology such ascarrier aggregation, or the like, which may contribute to extension of anetwork capacity. Further, in an asymmetric traffic structure in whichthe amount of downlink data is more than that of uplink data, the LAAmay provide an optimized LTE service according to various requirementsor environments. For convenience, the LTE technology in the licensed(alternatively, authorized or permitted) band is referred to asLTE-licensed (LTE-L) and the LTE technology in the unlicensed(alternatively, unauthorized, non-licensed, license-unnecessary) band isreferred to as LTE-unlicensed (LTE-U) or LAA.

FIG. 13 illustrates a layout scenario of a user equipment and a basestation in an LAA service environment. A frequency band targeted by theLAA service environment has a short wireless communication reachdistance due to a high-frequency characteristic. By considering this,the layout scenario of the user equipment and the base station in anenvironment in which the conventional LTE-L service and the LAA servicecoexist may be an overlay model and a co-located model.

In the overlay model, a macro base station may perform wirelesscommunication with an X UE and an X′ UE in a macro area (32) by using alicensed carrier and be connected with multiple radio remote heads(RRHs) through an X2 interface. Each RRH may perform wirelesscommunication with an X UE or an X′ UE in a predetermined area (31) byusing an unlicensed carrier. The frequency bands of the macro basestation and the RRH are different from each other not to interfere witheach other, but data needs to be rapidly exchanged between the macrobase station and the RRH through the X2 interface in order to use theLAA service as an auxiliary downlink channel of the LTE-L servicethrough the carrier aggregation.

In the co-located model, a pico/femto base station may perform thewireless communication with a Y UE by using both the licensed carrierand the unlicensed carrier. However, it may be limited that thepico/femto base station uses both the LTE-L service and the LAA serviceto downlink transmission. A coverage (33) of the LTE-L service and acoverage (34) of the LAA service may be different according to thefrequency band, transmission power, and the like.

When LTE communication is performed in the unlicensed band, conventionalequipments (e.g., wireless LAN (Wi-Fi) equipments) which performcommunication in the corresponding unlicensed band may not demodulate anLTE-U message or data and determine the LTE-U message or data as a kindof energy to perform an interference avoidance operation by an energydetection technique. That is, when energy corresponding to the LTE-Umessage or data is lower than −62 dBm or certain energy detection (ED)threshold value, the wireless LAN equipments may perform communicationby disregarding the corresponding message or data. As a result, thatuser equipment which performs the LTE communication in the unlicensedband may be frequently interfered by the wireless LAN equipments.

Therefore, a specific frequency band needs to be allocated or reservedfor a specific time in order to effectively implement an LTE-Utechnology/service. However, since peripheral equipments which performcommunication through the unlicensed band attempt access based on theenergy detection technique, there is a problem in that an efficientLTE-U service is difficult. Therefore, a research into a coexistencescheme with the conventional unlicensed band device and a scheme forefficiently sharing a radio channel needs to be preferentially made inorder to settle the LTE-U technology. That is, a robust coexistencemechanism in which the LTE-U device does not influence the conventionalunlicensed band device needs to be developed.

FIG. 14 illustrates a communication scheme (e.g., wireless LAN) thatoperates in an unlicensed band in the related art. Since most devicesthat operate in the unlicensed band operate based on listen-before-talk(LBT), a clear channel assessment (CCA) technique that senses a channelbefore data transmission is performed.

Referring to FIG. 14, a wireless LAN device (e.g., AP or STA) checkswhether the channel is busy by performing carrier sensing beforetransmitting data. When a predetermined strength or more of radio signalis sensed in a channel to transmit data, it is determined that thecorresponding channel is busy and the wireless LAN device delays theaccess to the corresponding channel. Such a process is referred to asclear channel evaluation and a signal level to decide whether the signalis sensed is referred to as a CCA threshold. Meanwhile, when the radiosignal is not sensed in the corresponding channel or a radio signalhaving a strength smaller than the CCA threshold is sensed, it isdetermined that the channel is idle.

When it is determined that the channel is idle, a terminal having datato be transmitted performs a back-off procedure after a defer period(e.g., arbitration interframe space (AIFS), PCF IFS (PIFS), or thelike). The defer period means a minimum time when the terminal needs towait after the channel is idle. The back-off procedure allows theterminal to further wait for a predetermined time after the deferperiod. For example, the terminal stands by while decreasing a slot timefor slot times corresponding to a random number allocated to theterminal in the contention window (CW) during the channel is in an idlestate, and a terminal that completely exhausts the slot time may attemptto access the corresponding channel.

When the terminal successfully accesses the channel, the terminal maytransmit data through the channel When the data is successfullytransmitted, a CW size (CWS) is reset to an initial value (CWmin). Onthe contrary, when the data is unsuccessfully transmitted, the CWSincreases twice. As a result, the terminal is allocated with a newrandom number within a range which is twice larger than a previousrandom number range to perform the back-off procedure in a next CW. Inthe wireless LAN, only an ACK is defined as receiving responseinformation to the data transmission. Therefore, when the ACK isreceived with respect to the data transmission, the CWS is reset to theinitial value and when feed-back information is not received withrespect to the data transmission, the CWS increases twice.

As described above, since most communications in the unlicensed band inthe related art operate based on the LBT, the LTE also considers the LBTin the LAA for coexistence with the conventional device. In detail, inthe LTE, the channel access method on the unlicensed band may be dividedinto 4 following categories according to the presence/an applicationscheme of the LBT.

-   -   Category 1: No LBT    -   An LBT procedure by a Tx entity is not performed.    -   Category 2: LBT without Random Back-Off    -   A time interval in which the channel needs to be sensed in an        idle state before the Tx entity performs a transmission on the        channel is decided. The random back-off is not performed.    -   Category 3: LBT with Random Back-Off with a CW of Fixed Size    -   LBT method that performs random back-off by using a CW of a        fixed size. The Tx entity has a random number N in the CW and        the CW size is defined by a minimum/maximum value of N. The CW        size is fixed. The random number N is used to decide the time        interval in which the channel needs to be sensed in an idle        state before the Tx entity performs a transmission on the        channel.    -   Category 4: LBT with Random Back-Off with a CW of Variable Size    -   LBT method that performs the random back-off by using a CW of a        variable size. The Tx entity has the random number N in the CW        and the CW size is defined by the minimum/maximum value of N.        The Tx entity may change the CW size at the time of generating        the random number N. The random number N is used to decide the        time interval in which the channel needs to be sensed in an idle        state before the Tx entity performs a transmission on the        channel

FIGS. 15 and 16 illustrate a DL transmission process based on thecategory 4 LBT. The category 4 LBT may be used to guarantee fair channelaccess with Wi-Fi. Referring to FIGS. 15 and 16, the LBT processincludes initial CCA (ICCA) and extended CCA (ECCA). In the ICCA, therandom back-off is not performed and in the ECCA, the random back-off isperformed by using the CW of the variable size. The ICCA is applied tothe case in which the channel is idle when signal transmission isrequired and the ECCA is applied to the case in which the channel isbusy when the signal transmission is required or DL transmission isperformed just before. That is, it is determined whether the channel isidle through the ICCA, and data transmission is performed after the ICCAperiod. If the interference signal is detected and data transmissionfails, a data transmission time point may be obtained through a deferperiod+backoff counter after setting a random backoff counter.

Referring to FIG. 15, a signal transmitting process may be performed asfollows.

Initial CCA

-   -   S1202: The base station verifies that the channel is idle.    -   S1204: The base station verifies whether the signal transmission        is required. When the signal transmission is not required, the        process returns to S202 and when the signal transmission is        required, the process proceeds to S1206.    -   S1206: The base station verifies whether the chanel is idle for        an ICCA defer period (B_(CCA)). The ICCA defer period is        configurable. As an implementation example, the ICCA defer        period may be constituted by an interval of 16 μs and n        consecutive CCA slots. Herein, n may be a positive integer and        one CCA slot interval may be 9 μs. The number of CCA slots may        be configured differently according to a QoS class. The ICCA        defer period may be set to an appropriate value by considering a        defer period (e.g., DIFS or AIFS) of Wi-Fi. For example, the        ICCA defer period may be 34 us. When the channel is idle for the        ICCA defer period, the base station may perform the signal        transmitting process (S1208). When it is determined that the        channel is busy during the ICCA defer period, the process        proceeds to S1212 (ECCA).    -   S1208: The base station may perform the signal transmitting        process. When the signal transmission is not performed, the        process proceeds to S1202 (ICCA) and when the signal        transmission is performed, the process proceeds to S1210. Even        in the case where a back-off counter N reaches 0 in S1218 and        S1208 is performed, when the signal transmission is not        performed, the process proceeds to S1202 (ICCA) and when the        signal transmission is performed, the process proceeds to S1210.    -   S1210: When additional signal transmission is not required, the        process proceeds to S1202 (ICCA) and when the additional signal        transmission is required, the process proceeds to S1212 (ECCA).

Extended CCA

-   -   S1212: The base station generates the random number N in the CW.        N is used as a counter during the back-off process and generated        from [0, q-1]. The CW may be constituted by q ECCA slots and an        ECCA slot size may be 9 μs or 10 μs. The CW size (CWS) may be        defined as q and be variable in S1214. Thereafter, the base        station proceeds to S1216.    -   S1214: The base station may update the CWS. The CWS q may be        updated to a value between X and Y. The X and Y values are        configurable parameters. CWS update/adjustment may be performed        whenever N is generated (dynamic back-off) and semi-statically        performed at a predetermined time interval (semi-static        back-off). The CWS may be updated/adjusted based on exponential        back-off or binary back-off. That is, the CWS may be        updated/adjusted in the form of the square of 2 or the multiple        of 2. In association with PDSCH transmission, the CWS may be        updated/adjusted based on feed-back/report (e.g., HARQ ACK/NACK)        of the user equipment or updated/adjusted based on base station        sensing.    -   S1216: The base station verifies whether the channel is idle for        an ECCA defer period (DeCCA). The ECCA defer period is        configurable. As an implementation example, the ECCA defer        period may be constituted by an interval of 16 μs and n        consecutive CCA slots. Herein, n may be a positive integer and        one CCA slot interval may be 9 μs. The number of CCA slots may        be configured differently according to the QoS class. The ECCA        defer period may be set to the appropriate value by considering        the defer period (e.g., DIFS or AIFS) of Wi-Fi. For example, the        ECCA defer period may be 34 us. When the channel is idle for the        ECCA defer period, the base station proceeds to S1218. When it        is determined that the channel is busy during the ECCA defer        period, the base station repeats S1216.    -   S1218: The base station verifies whether N is 0. When N is 0,        the base station may perform the signal transmitting process        (S1208). In this case, (N=0), the base station may not        immediately perform transmission and performs CCA check for at        least one slot to continue the ECCA process. When N is not 0        (that is, N>0), the process proceeds to S1220.    -   S1220: The base station senses the channel during one ECCA slot        interval (T). The ECCA slot size may be 9 μs or 10 μs and an        actual sensing time may be at least 4 μs.    -   S1222: When it is determined that the channel is idle, the        process proceeds to S1224. When it is determined that the        channel is busy, the process returns to S1216. That is, one ECCA        defer period is applied again after the channel is idle and N is        not counted during the ECCA defer period.    -   S1224: N is decreased by 1 (ECCA countdown).

FIG. 16 is substantially the same as/similar to the transmitting processof FIG. 15 and is different from FIG. 15 according to an implementationscheme. Therefore, detailed matters may be described with reference tocontents of FIGS. 15.

-   -   S1302: The base station verifies whether the signal transmission        is required. When the signal transmission is not required, S1302        is repeated and when the signal transmission is required, the        process proceeds to S1304.    -   S1304: The base station verifies whether the slot is idle. When        the slot is idle, the process proceeds to S1306 and when the        slot is busy, the process proceeds to S1312 (ECCA). The slot may        correspond to the CCA slot in FIGS. 15.    -   S1306: The base station verifies whether the channel is idle for        a defer period (D). D may correspond to the ICCA defer period in        FIG. 15. When the channel is idle for the defer period, the base        station may perform the signal transmitting process (S1308).        When it is determined that the channel is busy during the defer        period, the process proceeds to S1304.    -   S1308: The base station may perform the signal transmitting        process if necessary.    -   S1310: When the signal transmission is not performed, the        process proceeds to S1302 (ICCA) and when the signal        transmission is performed, the process proceeds to S1312 (ECCA).        Even in the case where the back-off counter N reaches 0 in S1318        and S1308 is performed, when the signal transmission is not        performed, the process proceeds to S1302 (ICCA) and when the        signal transmission is performed, the process proceeds to S1312        (ECCA).

Extended CCA

-   -   S1312: The base station generates the random number N in the CW.        N is used as the counter during the back-off process and        generated from [0, q-1]. The CW size (CWS) may be defined as q        and be variable in S1314. Thereafter, the base station proceeds        to S1316.    -   S1314: The base station may update the CWS. The CWS q may be        updated to the value between X and Y. The X and Y values are        configurable parameters. CWS update/adjustment may be performed        whenever N is generated (dynamic back-off) and semi-statically        performed at a predetermined time interval (semi-static        back-off). The CWS may be updated/adjusted based on exponential        back-off or binary back-off. That is, the CWS may be        updated/adjusted in the form of the square of 2 or the multiple        of 2. In association with PDSCH transmission, the CWS may be        updated/adjusted based on feed-back/report (e.g., HARQ ACK/NACK)        of the user equipment or updated/adjusted based on base station        sensing.    -   S1316: The base station verifies whether the channel is idle for        the defer period (D). D may correspond to the ECCA defer period        in FIG. 15. D in S1306 and D in S1316 may be the same as each        other. When the channel is idle for the defer period, the base        station proceeds to S1318. When it is determined that the        channel is busy during the defer period, the base station        repeats S1316.    -   S1318: The base station verifies whether N is 0. When N is 0,        the base station may perform the signal transmitting process        (S1308). In this case, (N=0), the base station may not        immediately perform transmission and performs CCA check during        at least one slot to continue the ECCA process. When N is not 0        (that is, N>0), the process proceeds to S1320.    -   S1320: The base station selects one of an operation of        decreasing N by 1 (ECCA count-down) and an operation of not        decreasing N (self-defer). The self-defer operation may be        performed according to implementation/selection of the base        station and the base station does not perform sensing for energy        detection and not perform even ECCA countdown in the self-defer.    -   S1322: The base station may select one of the operation not        performing sensing for energy detection and the energy detecting        operation. When the sensing for the energy detection is not        performed, the process proceeds to S1324. When the energy        detecting operation is performed, if an energy level is equal to        or lower than an energy detection threshold (that is, idle), the        process proceeds to S1324. If the energy level is higher than        the energy detection threshold (that is, busy), the process        returns to S1316. That is, one defer period is applied again        after the channel is idle and N is not counted during the defer        period.    -   S1324: The process proceeds to S1318.

FIG. 17 illustrates an example in which a base station performs DLtransmission in an unlicensed band. The base station may aggregate cells(for convenience, LTE-L cell) of one or more licensed bands and cells(for convenience, LTE-U cell) of one or more unlicensed bands. In FIG.17, a case in which one LTE-L cell and one LTE-U cell are aggregated forcommunication with the user equipment is assumed. The LTE-L cell may bethe PCell and the LTE-U cell may be the SCell. In the LTE-L cell, thebase station may exclusively use the frequency resource and perform anoperation depending on LTE in the related art. Therefore, all of theradio frames may be constituted by regular subframes (rSF) having alength of 1 ms (see FIG. 2) and the DL transmission (e.g., PDCCH andPDSCH) may be performed every subframe (see FIG. 1). Meanwhile, in theLTE-U cell, the DL transmission is performed based on the LBT forcoexistence with the conventional device (e.g., Wi-Fi device). Further,a specific frequency band needs to be allocated or reserved for aspecific time in order to effectively implement the LTE-Utechnology/service. Therefore, in the LTE-U cell, the DL transmissionmay be performed through a set of one or more consecutive subframes (DLtransmission burst) after the LBT. The DL transmission burst may startas the regular subframe (rSF) or a partial subframe (pSF) according toan LBT situation. pSF may be a part of the subframe and may include asecond slot of the subframe. Further, the DL transmission burst may endas rSF or pSF.

Hereinafter, DRS transmission in an unlicensed band will be described.Using Rel-12 DRS on carriers within the unlicensed band introduces newlimitations. LBT regulation in some areas treats DRS as a short controltransmission, allowing DRS transmission without LBT. However, in someareas (such as Japan), LBT is also required for short controltransmissions. Therefore, it is required to apply the LBT to the DRStransmission on the LAA SCELL.

FIG. 18 illustrates DRS transmission in an unlicensed band. When LBT isapplied to DRS transmission, DRS may not be periodically transmitted dueto LBT failure in the unlicensed band, unlike Rel-12 DRS transmitted inthe licensed band. If the DRS transmission fails within the DMTC, thefollowing two options may be considered.

-   -   Alt1: The DRS may only be transmitted at a fixed time point        within the DMTC. Therefore, when the DRS transmission fails,        there is no DRS transmission in the DMTC.    -   Alt2: The DRS may be transmitted in at least one other time        point within the DMTC. Thus, when a DRS transmission fails, a        DRS transmission may be attempted at another time point within        the DMTC.

Hereinafter, DRS transmission in an unlicensed band will be described.Specifically, a parameter for DRS transmission suitable for LAA based onDRS of 3GPP LTE Rel-12, a DRS transmission method, and the like aresuggested. For convenience, DRS in the existing licensed band isreferred to as Rel-12 DRS or LTE-L DRS, and DRS in the unlicensed bandis referred to as LAA DRS or LTE-U DRS.

FIG. 19 illustrates a parameter for LAA DRS transmission and a DRStransmission method based on LBT. The DRS transmission period isconfigured by the DMTC, and the DMTC period in the Rel-12 DRS isconfigured to 40/80/160 ms (see FIG. 8). However, when the channel ofthe transmission time point is busy due to the peripheral interferenceor the like in the case of the DRS transmitted in the LAA based on theLBT, the DRS may not be transmitted according to the DRS transmissionperiod. Therefore, if the DMTC period is configured to the same as thatin the LAA DRS, the transmission frequency of the LAA DRS may belowered. Therefore, a new DMTC period is required in the LAA, and may beconfigured to 40 ms or less, for example. In addition, the base stationmay attempt to transmit DRS at least once within the DMTC period, andmay configure a duration such as the DMTC and may be configured totransmit DRS in the corresponding duration. Accordingly, since the userequipment expects DRS transmission only in the DMTC, DRSsearch/detection is performed only in the corresponding DMTC, therebyreducing the power consumption of the user equipment and the burden ofblind detection/decoding. When a DRS transmission occurs in the DMTC,the base station transmits a DRS configuration (e.g., a configurationwith CRS/PSS/SSS/CSI-RS in Rel-12) when the channel is idle after LBT.DRS transmission duration may be defined as DRS occasion duration. TheDRS occasion duration in Rel-12 may be configured to 1 to 5 ms. SinceLAA operates based on LBT, as the DRS length (=DRS occasion duration)becomes longer, the transmittable time point decreases, and in the caseof long DRS, continuous transmission is required so that idle durationdoes not occur in order to prevent the transmission of other basestations/terminals/Wi-Fi devices based on LBT. FIG. 19 shows a DRSoccasion duration having a length of at least one subframe forconvenience, but the length of the DRS occasion duration is not limitedthereto. A method of transmitting DRS after LBT is broadly classifiedinto two. There are an Alt1 (DRS Alt. 1) technique, which allowstransmission from a fixed location (for convenience, the DMTC startinglocation) in the DMTC based on the LBT, and an Alt2 (DRS Alt. 2)technique, which allows at least one other DRS transmission even if theCCA result channel is busy in the DMTC and the DRS transmission fails.

FIG. 20 illustrates a case where simultaneous transmission of LAADRS+PDSCH occurs in SF #0/ #5 in the LAA DMTC, and FIG. 21 illustrates acase where simultaneous transmission of LAA DRS+PDSCH occurs in SFexcept for SF #0/#5 in LAA DMTC. SF #0/#5 represents SF #0 and/or SF #5.For illustration of the invention, although the drawing illustrates onlythe case where simultaneous transmission of LAA DRS+PDSCH occurs, in SFin the LAA DMTC, (i) only LAA DRS transmission (DRS alone transmission),(ii) only PDSCH transmission (PDSCH alone transmission), and (iii) LAADRS+PDSCH simultaneous transmission may be performed. WhenCRS/PSS/SSS/CSI-RS (CSI-RS may be used as DRS if it is configuredseparately for DRS) is transmitted for DRS, CRS/PSS/SSS/CSI-RS is usedfor the original purpose (e.g., L1 channel estimation (e.g., CSI), datademodulation, time/frequency synchronization, etc.) and RRM measurement(L3 channel estimation) and when CRS/PSS/SSS/CSI-RS is transmitted fornon-DRS, CRS/PSS/SSS/CSI-RS is used for the original purpose. Therefore,when a user equipment detects CRS/PSS/SSS/CSI-RS, user equipment shouldrecognize whether or not CRS/PSS/SSS/CSI-RS are transmitted as DRS.Also, when the PDSCH is transmitted from the SF in the LAA DMTC, theamount/location of the resource (i.e., RE) to which the PDSCH is mappedin the SF changes depending on (i) PDSCH alone transmission, or (ii) LAADRS+PDSCH simultaneous transmission. Therefore, in order to properlydecode the PDSCH, the user equipment is required to recognize whetherthe PDSCH is transmitted alone or with the LAA DRS in the correspondingSF.

Hereinafter, for the DL transmission in the unlicensed band, a methodand operation of a base station to allow a user equipment to recognize(i) whether LAA DRS exists (and/or whether LAA DRS is transmittedalone), (ii) LAA DRS+PDSCH is transmitted simultaneously, and (iii)whether PDSCH is transmitted alone will be described. In addition, forthe DL transmission in the unlicensed band, a method and operation of auser equipment to distinguish (i) whether LAA DRS exists (and/or whetherLAA DRS is transmitted alone), (ii) LAA DRS+PDSCH is transmittedsimultaneously, and (iii) whether PDSCH is transmitted alone will bedescribed. Hereinafter, DRS refers to the unlicensed band DRS (e.g., LAADRS) unless otherwise specified.

An explicit signaling method and an implicit signaling method arepossible as a method of a base station to allow a user equipment torecognize whether a LAA DRS exists. First, the following explicitsignaling method may be used.

Method 1) the base station may signal to the user equipment whether ornot DRS is present (of the LAA cell) through L1 signaling (e.g., PDCCH(DCI), common control channel, and PHICH) in the licensed band cell(e.g., PCell). For example, using a UE-specific DCI format or a commonDCI format in a PCell or a PHICH resource on a licensed band, the basestation may indicate to the user equipment whether or not there is DRSof the unlicensed band cell.

First, a method of indicating whether or not DRS is present to a userequipment using a user equipment-specific DCI format will be described.In cross-carrier scheduling, using DL Grant DCI format included in PCellPDCCH/EPDCCH, the base station schedules a DL transmission burst (e.g.,PDSCH) in the unlicensed band to the user equipment. Thus, by includingan indication bit (e.g., indicating the presence or absence of DRS) inthe DL grant DCI format that schedules the unlicensed band, the userequipment may recognize the presence of DRS in the unlicensed bandthrough the corresponding indication bit. Through this, for the SF ofthe unlicensed band (or DL transmission burst), the user equipment maydetermine (i) whether or not DRS is present (or whether DRS istransmitted alone), (ii) whether DRS+PDSCH is transmittedsimultaneously, (iii) whether PDSCH is transmitted alone. Accordingly,the base station may perform rate-matching/resource mapping inconsideration of the presence or absence of DRS when transmittingEPDCCH/PDSCH. Also, in consideration of the presence of DRS, as assumingbase station rate-matching/resource mapping according to the presence ofDRS, user equipment may also perform an EPDCCH/PDSCH decoding/decodingprocess (e.g., including or except information in the DRS RE duringdecoding/demodulating).

Next, the base station may inform the user equipment of the presence ofDRS using a common DCI. Since DRS is transmitted in a basestation-specific (BS-specific) manner in order for RRM measurement orcoarse/fine time/frequency synchronization, the presence or absence ofDRS is informed by using a control channel having a DCI that isCRC-scrambled by CC-RNTI, i.e., a common DCI so that user equipmentscapable of receiving a base station signal receive it in common. Throughsuch signaling, for the corresponding subframe, the user equipment maydetermine (i) whether or not DRS is present (or whether DRS istransmitted alone), (ii) whether DRS+PDSCH is transmittedsimultaneously, (iii) whether PDSCH is transmitted alone. Accordingly,the base station may perform rate-matching/resource mapping inconsideration of the presence or absence of DRS when transmittingEPDCCH/PDSCH. Also, in consideration of the presence of DRS, as assumingbase station rate-matching/resource mapping according to the presence ofDRS, user equipment may also perform an EPDCCH/PDSCHdecoding/demodulating process (e.g., including or except information onthe DRS RE during decoding/demodulating).

Finally, the PHICH resource in the licensed band may be used to indicateto the user equipment whether DRS is present. For uplink transmission inthe licensed band, since synchronous and non-adaptive retransmissionsare supported, a PHICH resource that transmits HARQ-ACK feedback isused. On the other hand, for uplink transmission in the unlicensed band,since asynchronous and adaptive retransmissions are supported, a PHICHresource that transmits is not used. On the other hand, in the case ofcross-carrier scheduling, when the existing procedure is followed, thePHICH is transmitted from the cell in which the UL grant is transmitted.Therefore, the PHICH resource for SCell (i.e., LAA SCell) in theunlicensed band is configured to be transmitted from the PCell in thelicensed band. However, for the uplink transmission in the LAA SCell,retransmission is indicated only through the PDCCH, PHICH resources forLAA SCell in PCell are not used. Therefore, it is possible to indicatewhether the DRS is transmitted in the LAA SCell using the PHICH resourcefor the LAA SCell in the PCell. Through such signaling, for thecorresponding subframe, the user equipment may determine (i) whether ornot DRS is present (or whether DRS is transmitted alone), (ii) whetherDRS+PDSCH is transmitted simultaneously, (iii) whether PDSCH istransmitted alone. Accordingly, the base station may performrate-matching/resource mapping in consideration of the presence orabsence of DRS when transmitting EPDCCH/PDSCH. Also, in consideration ofthe presence of DRS, as assuming base station rate-matching/resourcemapping according to the presence of DRS, user equipment may alsoperform an EPDCCH/PDSCH decoding/demodulating process (e.g., includingor except information on the DRS RE during decoding/demodulating).

Method 2) the base station may signal to the base station whether or notDRS is present through L1 signaling (e.g., PDCCH (DCI), common controlchannel, and PHICH) in the unlicensed band cell (e.g., LAA SCell). Forexample, using a UE-specific DCI format or a common DCI format in a LAASCell or a PHICH resource, the base station may indicate to the userequipment whether or not DRS is present.

First, a method of indicating whether or not DRS is present to a userequipment using a user equipment-specific DCI format will be described.When self-carrier scheduling is used, the base station includes anindication bit (e.g., indicating the presence or absence of DRS) in theDL grant DCI format of the PDCCH transmitted in the unlicensed band, sothat the user equipment may recognize the presence of DRS in theunlicensed band through the corresponding indication bit. Through this,for the SF of the unlicensed band (or DL transmission burst), the userequipment may determine (i) whether or not DRS is present (or whetherDRS is transmitted alone), (ii) whether DRS+PDSCH is transmittedsimultaneously, (iii) whether PDSCH is transmitted alone. Accordingly,the base station may perform rate-matching/resource mapping inconsideration of the presence or absence of DRS when transmittingEPDCCH/PDSCH. Also, in consideration of the presence of DRS, as assumingbase station rate-matching/resource mapping according to the presence ofDRS, user equipment may also perform an EPDCCH/PDSCHdecoding/demodulating process (e.g., including or except information onthe DRS RE during decoding/demodulating). When SCell (LAA SCell #1) inthe unlicensed band cross-carriers schedules another SCell (LAA SCell#2) in the unlicensed band, the base station schedules a DL transmissionburst (e.g., PDSCH) of LAA SCell #2 to the user equipment using the DLGrant DCI format included in the PDCCH/EPDCCH of LAA SCell #1. Thus, bythe DL grant DCI format of the LAA SCell#1 including an indication bit(e.g., indicating the presence or absence of DRS) in, the user equipmentmay recognize the presence of DRS in the LAA SCell#2 through thecorresponding indication bit. Through this, for the SF of the LAASCell#2 (or DL transmission burst), the user equipment may determine (i)whether or not DRS is present (or whether DRS is transmitted alone),(ii) whether DRS+PDSCH is transmitted simultaneously, (iii) whetherPDSCH is transmitted alone. Accordingly, the base station may performrate-matching/resource mapping in consideration of the presence orabsence of DRS when transmitting EPDCCH/PDSCH. Also, in consideration ofthe presence of DRS, as assuming base station rate-matching/resourcemapping according to the presence of DRS, user equipment may alsoperform an EPDCCH/PDSCH decoding/demodulating process (e.g., includingor except information on the DRS RE during decoding/demodulating).

Next, the base station may inform the user equipment of the presence ofDRS using a common DCI on the LAA SCell. Since DRS is transmitted in aBS-specific manner in order for RRM measurement or coarse/finetime/frequency synchronization, the presence or absence of DRS may beinformed by using a control channel having a DCI that is CRC-scrambledby CC-RNTI on the LAA SCell, i.e., a common DCI so that user equipmentscapable of receiving a base station signal to receive it in common.Through such signaling, for the corresponding subframe, the userequipment may determine (i) whether or not DRS is present (or whetherDRS is transmitted alone), (ii) whether DRS+PDSCH is transmittedsimultaneously, (iii) whether PDSCH is transmitted alone. Accordingly,the base station may perform rate-matching/resource mapping inconsideration of the presence or absence of DRS when transmittingEPDCCH/PDSCH. Also, in consideration of the presence of DRS, as assumingbase station rate-matching/resource mapping according to the presence ofDRS, user equipment may also perform an EPDCCH/PDSCHdecoding/demodulating process (e.g., including or except information onthe DRS RE during decoding/demodulating).

Finally, the PHICH resource in the unlicensed band may be used toindicate to the user equipment whether DRS is present. For uplinktransmission in the licensed band, since synchronous and non-adaptiveretransmissions are supported, a PHICH resource that transmits HARQ-ACKfeedback is used. On the other hand, for uplink transmission in thelicensed band, since asynchronous and adaptive retransmissions aresupported, a PHICH resource is not used. On the other hand, in the caseof cross-carrier scheduling, when the existing procedure is followed,the PHICH is transmitted from the cell in which the UL grant istransmitted. Therefore, the PHICH resource for the scheduled SCell inthe unlicensed band is configured in the scheduling SCell in theunlicensed band. Therefore, it is possible to indicate the DRStransmission in the scheduled SCell using the PHICH resource for thescheduled SCell in the scheduling SCell. Through such signaling, for thecorresponding subframe, the user equipment may determine (i) whether ornot DRS is present (or whether DRS is transmitted alone), (ii) whetherDRS+PDSCH is transmitted simultaneously, (iii) whether PDSCH istransmitted alone. Accordingly, the base station may performrate-matching/resource mapping in consideration of the presence orabsence of DRS when transmitting EPDCCH/PDSCH. Also, in consideration ofthe presence of DRS, as assuming base station rate-matching/resourcemapping according to the presence of DRS, user equipment may alsoperform an EPDCCH/PDSCH decoding/demodulating process (e.g., includingor except information on the DRS RE during decoding/demodulating). Also,in the case of the self-carrier scheduling, when the existing procedureis followed, the PHICH resource for the uplink transmission scheduledfrom the unlicensed band cell (e.g., LAA SCell #1) is configured on theLAA SCell #1. Therefore, it is possible to indicate the DRS transmissionfor the LAA SCell #1 using the PHICH resource on the LAA SCell #1.Through such signaling, for the corresponding subframe, the userequipment may determine (i) whether or not DRS is present (or whetherDRS is transmitted alone), (ii) whether DRS+PDSCH is transmittedsimultaneously, (iii) whether PDSCH is transmitted alone. Accordingly,the base station may perform rate-matching/resource mapping inconsideration of the presence or absence of DRS when transmittingEPDCCH/PDSCH. Also, in consideration of the presence of DRS, as assumingbase station rate-matching/resource mapping according to the presence ofDRS, user equipment may also perform an EPDCCH/PDSCHdecoding/demodulating process (e.g., including or except information onthe DRS RE during decoding/demodulating).

Also, using the implicit signaling method below, the base station maymake the user equipment aware of the presence of DRS that may betransmitted in the unlicensed band.

Method 3) In the DMTC, regardless of whether the DRS is transmitted fromthe base station, the user equipment may consider/assume that DRS isalways/may be present in the SF where DRS transmission is possible.Specifically, the user equipment in the DMTC configured to the userequipment may assume that PDSCH and the DRS are simultaneouslytransmitted and assumes the presence of DRS to perform rate-matching forEPDCCH/PDSCH. That is, DRS RE may always be considered indecoding/demodulating EPDCCH/PDSCH in DMTC (i.e., rate-matching isperformed considering DRS RE). Therefore, the user equipment does notneed to receive signaling on whether DRS is transmitted. However, whenthe user equipment performs DRS detection, e.g., SF includingCRS/PSS/SSS/CSI-RS (CSI-RS may be used as DRS if it is separatelyconfigured for DRS) detection once in the DMTC, the user equipmentassumes that a DRS transmission from the base station occurs in the SF,so that the user equipment does not need to consider the DRS RE duringdecoding/demodulation of the EPDCCH/PDSCH after the DRS detection in thecorresponding DMTC (i.e., rate-matching is not performed inconsideration of DRS RE). When the LBT is successful, since the DRStransmission from the base station is performed only once within theDMTC, when the user equipment detects DRS in the DMTC, it is notnecessary to consider the DRS presence for the EPDCCH/PDSCH transmissionof the remaining DL transmission bursts transmitted by the base station.Accordingly, when the user equipment performs DRS detection, e.g., SFincluding CRS/PSS/SSS/CSI-RS (CSI-RS may be used as DRS if it isseparately configured for DRS) detection once in the DMTC , the userequipment assumes that a DRS transmission from the base station occursin the SF, so that the user equipment does not need to consider the DRSRE during decoding/demodulation of the EPDCCH/PDSCH after DRS detectionin the corresponding DMTC (i.e., does not perform rate-matching inconsideration of DRS RE). However, when DRS detection, e.g., SFincluding CRS/PSS/SSS/CSI-RS (CSI-RS may be used as DRS if it isseparately configured for DRS) detection is not yet performed in theDMTC, the user equipment assumes the DRS presence in the SF where DRStransmission possibility exists and performs rate-matching onEPDCCH/PDSCH according to DRS RE mapping to performdecoding/demodulation of EPDCCH/PDSCH.

Before describing method 4), a secondary synchronization signal (SSS)sequence index according to a subframe index used in 3GPP Rel-8 toRel-12 will be described with reference to FIG. 22. Referring to FIG.22, the SSS sequence is composed of an SSS sequence 1 SSS₁ allocated toSF #0 and an SSS sequence 2 SSS₂ allocated to SF #0. SSS₁ and SSS₂ areboth composed of sequences X and Y, respectively. The sequences X and Yare alternately mapped to subcarriers. In SF #0, the sequence X ismapped first, and in SF #5, the sequence Y is mapped first. That is, theSSS is composed of a combination of the sequences X and Y, and themapping order of the sequences X and Y is changed according to the SFindex. For convenience, it is assumed that SSS₁ is composed of (sequenceX, sequence Y), and SSS₁ is composed of (sequence Y, sequence X). It isalso assumed that SSS₁ and SSS₂ have SSS sequence index 1 and SSSsequence index 2, respectively.

Method 4) through the detection of the index of the SSS constituting theDRS, the user equipment may recognize whether it is the DRS transmissionor the DRS+PDSCH simultaneous transmission. First, a method ofconfiguring a sequence index of SSS/CRS/CSI-RS (CSI-RS may be used asDRS when it is separately configured for DRS) constituting DRS will bedescribed (Option 1 to 4).

Option 1) when DRS is transmitted in SF #0 to #4 in DMTC, theSSS/CRS/CSI-RS sequence in the DRS may be obtained by applying the indexof SF #0 to the 3GPP Rel-12 SSS/CRS/CSI-RS sequence. When DRS istransmitted in SF #5 to #9 in DMTC, SSS/CRS/CSI-RS sequence in the DRSmay be obtained by applying the index of SF #5 to 3GPPRel-12SSS/CRS/CSI-RS sequence. Specifically, the 3GPP Rel-12SSS/CRS/CSI-RS sequence is provided based on the SF index of each SF.The SSS/CRS/CSI-RS sequence in DRS is provided based on the index of SF#0 or SF #5.

As an example, the 3GPP Rel-12 CRS sequence is generated by Equation 1.The initial value of the CRS sequence is given by Equation 2.

$\begin{matrix}{{{r_{l,n_{s}}(m)} = {{\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {2m} \right)}}} \right)} + {j\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {{2m} + 1} \right)}}} \right)}}},\mspace{20mu} {m = 0},1,\ldots \;,{{2N_{RB}^{\max,{DL}}} - 1}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Here, n_(s) represents a slot index in a radio frame, l represents anOFDMA symbol index in the slot, c(•) represents a pseudo-randomsequence, and N_(RB) ^(max,DL) represents the maximum number of RBs inthe DL band. c(•) is initialized using the initial value of Equation 2at the beginning of each OFDM symbol.

c _(init)=2¹⁰·(7·(n _(s)+1)+l+1)·(2·N _(ID) ^(cell)+1)+2·N _(ID) ^(cell)+N _(CP)   [Equation 2]

Here, n_(s) represents a slot index in a radio frame, l represents anOFDM symbol index in the slot, N_(ID) ^(cell) represents a physical cellID, N_(CP) represents a CP type, 1 for a normal CP and 0 for an extendedCP. The slot index n_(s) in the radio frame has the followingrelationship with the SF index SF #.

TABLE 2 SF # 0 1 2 3 4 5 6 7 8 9 n_(s) 0 1 2 3 4 5 6 7 8 9 10 11 12 1314 15 16 17 18 19

Since the initial value is determined based on each SF index in the 3GPPRel-12 CRS sequence, n_(s) of Equation 2 has a value of 0 to 19according to the SF to which the CRS is transmitted.

On the other hand, when the CRS is used as the DRS, n_(s) of Equation 2has only a slot index corresponding to the SF #0 or SF #5 according tothe SF to which the DRS is transmitted as follows.

TABLE 3 SF # 0 1 2 3 4 5 6 7 8 9 n_(s) 0 1 0 1 0 1 0 1 0 1 10 11 10 1110 11 10 11 10 11

As an example, the 3GPP Rel-12CSI-RS sequence is generated by Equation3. The initial value of the CSI-RS sequence is given by Equation 4.

$\begin{matrix}{{{r_{l,n_{s}}(m)} = {{\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {2m} \right)}}} \right)} + {j\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {{2m} + 1} \right)}}} \right)}}},\mspace{20mu} {m = 0},1,\ldots \;,{N_{RB}^{\max,{DL}} - 1}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

Here, n_(s) represents a slot index in a radio frame, l represents anOFDMA symbol index in the slot, c(•) represents a pseudo-randomsequence, and N_(RB) ^(max,DL) represents the maximum number of RBs inthe DL band. c(•) is initialized using the initial value of Equation 4at the beginning of each OFDM symbol.

c _(init)=2¹⁰·(7·(n _(s)+1)+l+1)·(2·N _(ID) ^(CSI)+1)+2·N _(ID) ^(CSI)+N _(CP)   [Equation 4]

Here, n_(s) represents a slot index in a radio frame, l represents anOFDM symbol index in a slot, N_(ID) ^(CSI) is configured by a higherlayer (e.g., RRC), and is equal to N_(ID) ^(cell) when not configured bya higher layer. N_(ID) ^(cell) represents a physical cell ID, and N_(CP)represents a CP type, 1 for a normal CP and 0 for an extended CP. Theslot index n_(s) in the radio frame has the relationship with the SFindex SF # as in Table 2.

Moreover, in the case where the CSI-RS is configured as DRS, the slotindexes n_(s) shown in Table 3 may be applied to Equation 3 and Equation4 for CSI-RS sequence generation in the same manner as applied in CRSused as DRS. That is, when the CSI-RS is used as the DRS, n_(s) ofEquation 4 has only a slot index corresponding to the SF #0 or SF #5according to the SF to which the DRS is transmitted as in Table 3.

Option 2) when DRS is transmitted in SF #0 to #4 in DMTC, the SSSsequence in the DRS may be obtained by applying the index of SF #0 tothe 3GPP Rel-12 SSS sequence (e.g., SSS₁ of FIG. 22). When DRS istransmitted in SF #5 to #9 in DMTC, the SSS sequence in the DRS may beobtained by applying the index of SF #5 to the 3GPP Rel-12555 sequence(e.g., SSS₂ of FIG. 22). On the other hand, the CRS/CSI-RS sequence inthe DRS may use the CRS/CSI-RS sequence generated according to each SFindex as in the method used in 3GPP Rel-12. That is, for the CRS as theDRS, the slot index n_(s) of Table 2 may be applied to Equation 2according to the transmitted SF, and for the CSI-RS of the DRS, the slotindex n_(s) of Table 2 may be applied to Equation 4 according to thetransmitted SF.

Option 3) when DRS is transmitted in DMTC, the SSS/CRS/CSI-RS sequencein the DRS may be obtained by applying the index of SF #0 to the 3GPPRel-12SSS/CRS/CSI-RS sequence. That is, unlike Option 1, when DRS istransmitted in DMTC, the SSS/CRS/CSI-RS sequence in the DRS may beobtained by always applying the index of SF #0 to the 3GPPRel-12SSS/CRS/CSI-RS sequence. That is, for the CRS as the DRS, the slotindex n_(s) of Table 4 may be applied to Equation 2 according to thetransmitted SF, and for the CSI-RS of the DRS, the slot index n_(s) ofTable 4 may be applied to Equation 4 according to the transmitted SF.

TABLE 4 SF # 0 1 2 3 4 5 6 7 8 9 n_(s) 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 01 0 1

Option 4) when DRS is transmitted in DMTC, the SSS sequence in the DRSmay be obtained by applying the index of SF #0 to the 3GPP Rel-12 SSSsequence. On the other hand, the CRS/CSI-RS sequence in the DRS may usethe CRS/CSI-RS sequence generated according to each SF index as in themethod used in 3GPP Rel-12. That is, for the CRS as the DRS, the slotindex n_(s) of Table 2 may be applied to Equation 2 according to thetransmitted SF, and for the CSI-RS as the DRS, the slot index n_(s) ofTable 2 may be applied to Equation 4 according to the transmitted SF.

Options 1) to 4) may be considered in DRS transmission irrespective ofPDSCH transmission. In order to distinguish between (i) whether or notDRS is present (or whether DRS is transmitted alone) and (ii) DRS+PDSCHsimultaneous transmission, for example, method 4) may swap the SSSsequence index to use an index different from the SSS sequence indexused for DRS during DRS+PDSCH simultaneous transmission. Accordingly,after detecting the SSS sequence index, the user equipment may recognizewhether the DRS transmission is performed or the DRS+PDSCH simultaneoustransmission is performed in the DL transmission burst in thecorresponding SF. Accordingly, through different SSS sequence indextransmissions at the base station and detection at the user equipment,for the SF (or DL transmission burst), the user equipment may determine(i) whether or not DRS is present (and/or whether DRS is transmittedalone), (ii) whether DRS+PDSCH is transmitted simultaneously, (iii)whether PDSCH is transmitted alone. Accordingly, the user equipment mayperform rate-matching for the PDSCH to perform decoding/demodulation ofthe EPDCCH/PDSCH.

An example in which method 4 is applied to Option 1) will be described.When DRS is transmitted in SF #0 to SF #4 in the DMTC, theSSS/CRS/CSI-RS sequence in DRS may be obtained by applying the index ofSF #0 to the 3GPP Rel-12SSS/CRS/CSI-RS sequence, and when DRS istransmitted in SF #5 to #9 in the DMTC, the SSS/CRS/CSI-RS sequence inDRS may be obtained by applying the index of SF #5 to the 3GPPRel-12SSS/CRS/CSI-RS sequence. However, when DRS+PDSCH simultaneoustransmission is performed in the DMTC, the SSS sequence index used in SF#5 instead of SF #0 is applied to the SSS sequences of SF #0 to #4(e.g., SSS₂ in FIG. 22) and the SSS sequence index used in SF #0 insteadof SF #5 may be applied to the SSS sequences of SF #5 to #9 (e.g., SSS₁in FIG. 22). Accordingly, through SSS detection, for the SF (or, DLtransmission burst), the user equipment may know whether (i) DRStransmission is performed or (ii) DRS+PDSCH simultaneous transmission isperformed.

An example in which method 4 is applied to Option 2) will be described.When DRS is transmitted alone in SF #0 to #9 in DMTC, the SSS sequencein the DRS may be obtained by applying the index of SF #0 to the 3GPPRel-12 SSS (e.g., SSS₁ of FIG. 22). On the other hand, when DRS+PDSCHsimultaneous transmission is performed in SF #0 to #4 in DMTC, the SSSsequence in the DRS may be obtained by applying the index of SF #5 tothe 3GPP Rel-12 SSS (e.g., SSS₂ of FIG. 22). Accordingly, through SSSdetection, for the SF (or, DL transmission burst), the user equipmentmay recognize whether (i) DRS transmission is performed or (ii)DRS+PDSCH simultaneous transmission is performed. When DRS istransmitted alone in SF #5 to #9 in DMTC, the SSS sequence in the DRSmay be obtained by applying the index of SF #5 to the 3GPP Rel-12555sequence (e.g., SSS₂ of FIG. 22). On the other hand, when DRS+PDSCHsimultaneous transmission is performed in SF #5 to #9 in DMTC, the SSSsequence in the DRS may be obtained by applying the index of SF #0 tothe 3GPP Rel-12 SSS (e.g., SSS₁ of FIG. 22). Accordingly, through SSSdetection, for the SF (or, DL transmission burst), the user equipmentmay recognize whether (i) DRS transmission is performed or (ii)DRS+PDSCH simultaneous transmission is performed.

An example in which method 4 is applied to Option 3) will be described.When DRS is transmitted in DMTC, the SSS/CRS/CSI-RS sequence in the DRSmay be obtained by applying the index of SF #0 to the 3GPP Rel-12SSS/CRS/CSI-RS sequence. On the other hand, when DRS+PDSCH simultaneoustransmission is performed in DMTC, the SSS sequence in the DRS may beobtained by applying the index of SF #5 to the 3GPP Rel-12 SSS (e.g.,SSS₂ of FIG. 22). Accordingly, through SSS detection, for the SF (or, DLtransmission burst), the user equipment may know whether (i) DRStransmission is performed or (ii) DRS+PDSCH simultaneous transmission isperformed.

An example in which method 4 is applied to Option 4) will be described.When DRS is transmitted in DMTC, the SSS sequence in the DRS may beobtained by applying the index of SF #0 to the 3GPP Rel-12 SSS sequence(e.g., SSS₁ of FIG. 22). On the other hand, when DRS+PDSCH simultaneoustransmission is performed in DMTC, the SSS sequence in the DRS may beobtained by applying the index of SF #5 to the 3GPP Rel-12555 (e.g.,SSS₂ of FIG. 22). Accordingly, through SSS detection, for the SF (or, DLtransmission burst), the user equipment may know whether (i) DRStransmission is performed or (ii) DRS+PDSCH simultaneous transmission isperformed.

Method 5) the user equipment may implicitly detect the presence of DRSby blind detection of CRS. For example, in SF #0/#5, a method ofallowing a user equipment to implicitly recognize whether a DRS ispresent through blind detection of a CRS may be considered. However, inthe case where DRS is transmitted in SF except for SF #0/#5, in order toverify whether or not DRS is present, detection of the CRS sequencegiven by the SF index is further required (e.g., option 1). The numberof blind detections of CRS may increase according to the configurationbetween an SF index and a CRS sequence belonging to DRS, but there areadvantages that in addition to not requiring additional signaling,whether DL transmission data burst is transmitted or not may berecognized by the blind detection of CRS.

Next, the PDSCH detection operation of the user equipment for the PDSCHtransmission based on the EPDCCH will be described. As considering acase where the DRS and the PDSCH are multiplexed in the SF #0/#5 in theDMTC, in the SF #0/#5, the user equipment may perform rate-matching inconsideration of DRS REs during decoding/demodulation of the PDSCH. Asconsidering a case where DRS and EPDCCH/PDSCH are multiplexed in SF#0/#5 in the DMTC, for the EPDCCH configure to be transmitted in thePDSCH region, it is not possible to signal the presence of DRS throughL1-signaling (e.g., DCI) over EPDCCH. That is, in the transmissionmethod/transmission mode for performing the EPDCCH-based PDSCHscheduling to the user equipment, when signaling for the presence orabsence of DRS through L1-signaling, this is because EPDCCH decodingmust be performed before knowing whether or not DRS is present. Thus,during EPDCCH decoding/demodulation, the user equipment may performrate-matching by always considering REs in which DRS may existregardless of whether or not DRS is present. On the other hand, duringPDSCH decoding/demodulation, the user equipment may performrate-matching by selectively considering DRS REs according to whether ornot DRS is present based on L1-signaling.

On the other hand, the transmission (e.g., (i) DRS alone transmission,(ii) DRS+PDSCH simultaneous transmission, (iii) PDSCH alonetransmission) (see FIG. 20) of the base station in SF #0/#5 in DMTC maybe different from the detection of the user equipment therefor. Inaddition, the transmission (e.g., (i) DRS alone transmission, (ii)DRS+PDSCH simultaneous transmission, (iii) PDSCH alone transmission)(see FIG. 21) of the base station in SF except SF #0/#5 in DMTC may bedifferent from the detection of the user equipment therefor. Thesolution to this problem is described below.

First, under the assumption of methods for enabling the user equipmentto recognize the presence of the DRS presented in the present invention,as shown in FIG. 20, the transmission (e.g., (i) DRS alone transmission,(ii) DRS+PDSCH simultaneous transmission, (iii) PDSCH alonetransmission) of the base station in SF #0/#5 in DMTC is described. Whenan indication is received that DRS is present in SF #0/#5, since PDSCHtransmission may occur simultaneously with DRS in the DL transmissionburst of SF #0/#5, the user equipment may be required to determinewhether DRS transmission only occurs in the DL transmission burst of SF#0/#5, or DRS+PDSCH simultaneous transmission occurs. This determinationmay be made as the user equipment blind-decodes the PDCCH/EPDCCH. As aresult of PDCCH/EPDCCH blind decoding, when there is a DL granttransmitted to the user equipment, the user equipment may performrate-matching on the DRS RE in considering that DRS+PDSCH simultaneoustransmission is performed from the base station to performdecoding/demodulation of the PDSCH. On the other hand, as a result ofthe PDCCH/EPDCCH blind decoding, when there is no DL grant transmittedto the user equipment, the user equipment may determine that DRS alonetransmission is performed and perform DRS detection. Also, since thereis no DRS in the DL transmission burst of SF #0/#5, when there is a DLgrant transmitted to the corresponding user equipment as a result ofPDCCH/EPDCCH blind decoding, a user equipment receiving an indicationthat there is no DRS in SF #0/#5 may perform decoding/demodulation ofthe PDSCH without operation like rate-matching for DRS RE.

In addition, a detection method of a user equipment for the transmission(e.g., (i) DRS alone transmission, (ii) DRS+PDSCH simultaneoustransmission, (iii) PDSCH alone transmission) (see FIG. 21) of the basestation in SF except SF #0/#5 is described. A user equipment thatreceives an indication that DRS is present in SF except SF #0/#5 mayfirst discriminate whether a DRS alone transmission is performed throughblind detection of CRS in SF except SF #0/#5 (e.g., option 1). Since DRSand PDSCH transmission may occur simultaneously in the DL transmissionburst in SF except SF #0/#5, the user equipment may blind-decode thePDCCH , in SF except SF #0/#5, to rate-match the DRS RE to performdecoding/demodulation of the PDSCH when there is a DL grant transmittedto the user equipment. Otherwise, the user equipment blind-decode thePDCCH to determine DRS alone transmission and perform DRS detection whenthere is no DL grant transmitted to the user equipment. Also, since DRSis not present in the DL transmission burst of the corresponding SF,when there is a DL grant transmitted to the corresponding user equipmentas a result of PDCCH/EPDCCH blind decoding, a user equipment receivingan indication that DRS is not present in SF except SF #O/#5 may performdecoding/demodulation of the PDSCH without operation like rate-matchingfor DRS RE.

During LAA operation, when the base station is configured to performdownlink transmission on the LAA SCell after the LBT success, the userequipment receives the subframe configuration information through commoncontrol signaling transmitted from the base station on the LAA SCell andperforms reception of physical channels and signals in the correspondingsubframe. Here, the common control signaling includes a PDCCH with auser equipment-common DCI, for example, a PDCCH with a DCI that isCRC-scrambled by a Common Control RNTI (CC-RNTI).

Table 5 shows subframe configuration information (subframe configurationfor LAA) in common control signaling. The subframe configurationinformation represents the occupied OFDM symbol configuration/number ofthe current subframe and the next subframe. The OFDM symbols occupied inthe subframe are used for transmission of DL physical channels and/orphysical signals.

TABLE 5 Value of Configuration of occupied OFDM ‘Subframe configurationfor LAA’ symbols field in current subframe (current subframe, nextsubframe) 0000 (—, 14) 0001 (—, 12) 0010 (—, 11) 0011 (—, 10) 0100 (—,9)  0101 (—, 6)  0110 (—, 3)  0111 (14, *)  1000 (12, —) 1001 (11, —)1010 (10, —) 1011  (9, —) 1100  (6, —) 1101  (3, —) 1110 reserved 1111reserved NOTE: (—, Y) means UE may assume the first Y symbols areoccupied in next subframe and other symbols in the next subframe are notoccupied. (X, —) means UE may assume the first X symbols are occupied incurrent subframe and other symbols in the current subframe are notoccupied. (X, *) means UE may assume the first X symbols are occupied incurrent subframe, and at least the first OFDM symbol of the nextsubframe is not occupied.

When the user equipment detects a PDCCH having a DCI CRC scrambled withCC-RNTI in SF #(n−1) or SF #n of the LAA SCell, the corresponding userequipment assumes the number of OFDM symbols occupied in the SF #n ofthe LAA SCell according to the subframe configuration information in theDCI detected in SF #(n−1) or SF #n. When the configuration of the OFDMsymbol occupied for SF #n is indicated by the subframe configurationinformation of SF #(n−1) and SF #n, the user equipment may assume thatthe subframe configuration information of SF #(n−1) and SF #n indicatesthe same information.

On the other hand, conventionally, common control signaling is notdetected in SF #(n−1) and common control signaling is detected in SF #n.When the number of occupied OFDM symbols of SF #n indicated by thecommon control signaling of SF #n (i.e., the LAA subframe structure) issmaller than 14, the user equipment does not (or does not need to)perform the reception of the physical channels/signals of the SF #n.From the viewpoint of receiving downlink data (e.g., PDSCH), even if theuser equipment does not perform/assume PDSCH reception due to mismatchof the common control signal, HARQ retransmissions do not causesignificant deterioration in system performance. The same is for acontrol channel (e.g., a PDCCH with DL grant DCI) that schedulesdownlink data (e.g., PDSCH). However, from the viewpoint of RRMmeasurement and time/frequency synchronization occurring periodically oraperiodically, if the user equipment does not perform RRM measurementand time/frequency synchronization due to mismatch of the common controlsignal, a great deterioration in system performance may occur.

To solve this problem, a method in which a user equipment performs RRMmeasurement and time/frequency synchronization according toreception/detection of common control signaling and LAA subframeconfiguration information is described. This example may be applied whenthe DL transmission is configured to be performed in the LAA SCell afterthe LBT.

First, DRS transmission for RRM measurement will be described. When DLtransmission is configured to be performed in the LAA SCell after LBT,the user equipment may not detect common control signaling (e.g.,indicating the configuration of the ending partial SF) in the SF #(n−1)of the LAA SCell and may detect common control signaling only in the SF#n of the LAA SCell. Here, the Ending SF indicates SF #n based on thecommon control signaling of SF #(n−1). Accordingly, the configuration ofSF #n is limited to partial SF (i.e., the number of OFDM symbols is lessthan 14). In this case, when SF #n is included in the DMTC of the userequipment, the user equipment may perform DRS detection on theassumption that DRS is transmitted in SF #n, and perform RRM measurementaccording to the DRS detection result. Here, the DRS signal may includeat least one of PSS, SSS, CRS, and CSI-RS (see FIGS. 20 and 21). Inaddition, the DMTC configures user equipment-specific using the DMTCtransmission period and the DMTC offset (SF unit) (see FIG. 8). On theother hand, under the same condition, the user equipment may not performthe reception process for physical channels other than DRS (e.g., PDCCH,EPDCCH, and PDSCH for downlink transmission) in SF #n (i.e., omit thereceiving process).

Additionally, when the number of occupied OFDM symbols of SF #nindicated by the common control signaling of SF #n (i.e., the LAA SFconfiguration) is not more than 12 OFDM symbols on which DRStransmission may be assumed based, for the transmission of DRSconsisting of 12 OFDM symbols, the user equipment may recognize throughthe SF configuration that no DRS transmission is performed from the basestation in SF #n. Therefore, the user equipment may not assume DRStransmission from the base station in SF #n, and may not perform DRSdetection in SF #n. That is, only when the SF configuration informationindicates that the number of OFDM symbols occupied in the SF #n is 12 ormore, the user equipment may perform DRS detection assuming DRStransmission from the base station.

Next, transmission of PSS/SSS performing time/frequency synchronizationwill be described. When DL transmission is configured to be performed inthe LAA SCell after LBT, the user equipment may not detect commoncontrol signaling (e.g., indicating the configuration of the endingpartial SF) in the SF #(n−1) of the LAA SCell and may detect commoncontrol signaling only in the SF #n of the LAA SCell. Here, the EndingSF indicates SF #n based on the common control signaling of SF #(n−1).Accordingly, the configuration of SF #n is limited to partial SF (i.e.,the number of OFDM symbols is less than 14). In this case, when SF #n isSF #0/#5, the user equipment may perform time/frequency synchronizationassuming PSS/SSS transmission in SF #n. On the other hand, under thesame condition, the user equipment may not perform the reception processfor physical channels other than DRS (e.g., PDCCH, EPDCCH, and PDSCH fordownlink transmission) in SF #n (i.e., omit the receiving process).

Additionally, when the number of occupied OFDM symbols of SF #nindicated by the common control signaling (i.e., LAA SF configuration)of SF #n is seven or more, since PSS/SSS may be transmitted, the userequipment may perform PSS/SSS detection only in that case. On the otherhand, when the number of occupied OFDM symbols of SF #n indicated by thecommon control signaling (i.e., LAA SF configuration) of SF #n is six orless, the user equipment may recognize that the PSS transmission may notbe performed in the SF #n through the SF configuration. Therefore, theuser equipment may not perform the PSS/SSS detection operation even ifthe SF #n is SF #0/#5. Since PSS is transmitted at OFDM symbol index #6and SSS is transmitted at OFDM symbol index #5, when the number ofoccupied OFDM symbols in SF #n is 6 or less, the user equipment mayassume that the PSS/SSS is not transmitted from the base station in theSF #n and may not perform the PSS/SSS detection operation in the SF #n(i.e., omit the PSS/SSS detection operation).

As another example, when DL transmission is configured to be performedon the LAA SCell after LBT, regardless of the number of occupied OFDMsymbols of SF #n indicated by common control signaling (i.e., LAA SFconfiguration) for PSS/SSS transmission of SF #0/#5, user equipment mayperform PSS/SSS detection process in SF #0/#5 and perform time/frequencysynchronization according to the detection result of PSS/SSS, assumingthat PSS/SSS is transmitted from base station.

FIG. 23 illustrates a downlink receiving process according to anembodiment of the present invention. This example may be applied whenthe DL transmission is configured to be performed on the LAA SCell afterthe LBT.

Referring to FIG. 23, the user equipment may monitor a first commoncontrol channel indicating downlink (DL) interval of SF #(n−1) and SF #n(S2302). The DL interval of SF #(n−1) and SF #n may be indicated by thenumber of OFDMs (available for DL transmission) and may be indicatedusing the subframe configuration information of Table 4. Also, the userequipment may monitor the second common control channel indicating theDL interval of SF #n and SF #(n+1) (S2304). The DL interval of SF #n andSF #(n+1) may be indicated by the number of OFDMs (available for DLtransmission) and may be indicated using the subframe configurationinformation of Table 4. Here, the first common control channel may bemonitored in SF #(n−1), and the second common control channel may bemonitored in SF #n. Also, SF #n may be included in the time window inwhich DRS reception is expected. Here, the time window for expecting DRSreception may include a DMTC, and the DMTC may be configured on a cellof an unlicensed band. In addition, the first and second common controlchannels may include a PDCCH in which the CRC is scrambled by theCC-RNTI.

Thereafter, the user equipment may perform/control the DL receptionprocess in the SF #n based on the detection results of the first andsecond common control channels (S2306). Here, when the user equipmentfails to detect the first common control channel, the detection of thesecond common control channel is successful, and the number of OFDMsymbols occupied for the SF #n indicated by the DL subframeconfiguration information in the SF #n through the detected commoncontrol channel is a part of the total OFDM symbols of the SF #n (i.e.,partial SF), for the downlink reception process of the user equipment inthe SF #n, only the detection process for the first physicalchannel/signal may be allowed. Here, the first physical channel/signalincludes DRS. In this case, the reception process for the secondphysical channel/signal in the SF #n may be omitted. Here, the secondphysical channel/signal may include a PDCCH, an EPDCCH, and a PDSCH fordownlink transmission. The PDCCH for uplink transmission may be includedin the first physical channel/signal.

On the other hand, when the user equipment fails to detect the firstcommon control channel, the detection of the second common controlchannel is successful, and the number of OFDM symbols occupied for theSF #n indicated by the DL subframe configuration information in the SF#n through the detected common control channel is 14 or less, that is, apart of the SF #n (i.e., partial SF), for the downlink reception processof the user equipment in the SF #n, only the detection process for thefirst physical channel/signal may be allowed. Here, the first physicalchannel/signal includes DRS. In this case, the reception process for thesecond physical channel/signal in the SF #n may be omitted. Here, thesecond physical channel/signal may include a PDCCH, an EPDCCH, and aPDSCH for downlink transmission.

On the other hand, when the user equipment fails to detect the firstcommon control channel, the detection of the second common controlchannel is successful, and the number of OFDM symbols occupied for theSF #n indicated by the DL subframe configuration information in the SF#n through the detected common control channel is 12, for the downlinkreception process of the user equipment in the SF #n, only the detectionprocess for the first physical channel/signal may be allowed. Here, thefirst physical channel/signal includes DRS. In this case, the receptionprocess for the second physical channel/signal in the SF #n may beomitted. Here, the second physical channel/signal may include a PDCCH,an EPDCCH, and a PDSCH for downlink transmission.

On the other hand, when the user equipment fails to detect the firstcommon control channel, the detection of the second common controlchannel is successful, and the number of OFDM symbols occupied for theSF #n indicated by the DL subframe configuration information in the SF#n through the detected common control channel is 12 or less, thereception process for other physical channels/signals including DRS inthe SF #n may be omitted. Here, a physical channel/signal other than DRSmay include a PDCCH, an EPDCCH, and a PDSCH for downlink transmission.

On the other hand, if the detection of the first common control channelfails, the detection of the second common control channel is successful,and the DL interval of SF #n is all of SF #n (i.e., full SF), thedownlink reception/detection process of the user equipment in the SF #nmay be normally performed/allowed for all channels/signals (e.g., DRS,PDCCH, EPDCCH, and PDSCH). Also, if both the first and second commoncontrol channels are successfully detected, regardless of whether the DLinterval of SF #n is a part of SF #n or not, the downlinkreception/detection process of the user equipment in the SF #n may benormally performed/allowed for all channels/signals (e.g., DRS, PDCCH,EPDCCH, and PDSCH).

FIG. 24 illustrates a configuration of a user equipment and a basestation according to an embodiment of the present invention. Theembodiment of the present invention, the user equipment may beimplemented by various types of wireless communication devices orcomputing devices that are guaranteed to be portable and mobility. Theuser equipment may be refered to as a station (STA), an MobileSubscriber (MS), or the like. In the embodiment of present invention,the base station may control and manage a cell (eg, macrocell,femtocell, picosell, etc.) corresponding to a service area and performfunction such as transmitting signal, designating channel, monitoringchannel, self-diagnosis, relay. The base station may be referred to asan evolved NodeB(eNB), an access point (AP), or the like.

Referring to FIG. 24, the user equipment 100 may include a processor110, a communication module 120, a memory 130, a user interface unit140, and a display unit 150.

The processor 110 may execute various commands or programs according tothe present invention and process data in the user equipment 100.Further, the processor 100 may control all operations of the respectiveunits of the user equipment 100 and control data transmission/receptionamong the units. For example, the processor 110 may receive/process thedownlink signal according to the proposal of the present invention. (SeeFIGS. 1 to 23.)

The communication module 120 may be an integrated module that performsmobile communication using a mobile communication network and wirelessLAN access using a wireless LAN. To this end, the communication module120 may include a plurality of network interface cards such as cellularcommunication interface cards 121 and 122 and a wireless LAN interfacecard 123 in an internal or external type. In the figure, thecommunication module 120 is illustrated as the integrated module, butthe respective network interface cards may be independently disposedaccording to a circuit configuration or a purpose unlike the figure.

The cellular communication interface card 121 transmits/receives a radiosignal to/from at least one of a base station 200, an external device,and a server by using the mobile communication networkand provides acellular communication service at a first frequency band based on acommand of the processor 110. The cellular communication interface card121 may include at least one NIC module using an LTE-licensed frequencyband. The cellular communication interface card 122 transmits/receivesthe radio signal to/from at least one of the base station 200, theexternal device, and the server by using the mobile communicationnetwork and provides the cellular communication service at a secondfrequency band based on the command of the processor 110. The cellularcommunication interface card 122 may include at least one NIC moduleusing an LTE-unlicensed frequency band. For example, the LTE-unlicensedfrequency band may be a band of 2.4 GHz or 5 GHz.

The wireless LAN interface card 123 transmits/receives the radio signalto/from at least one of the base station 200, the external device, andthe server through wireless LAN access and provides a wireless LANservice at the second frequency band based on the command of theprocessor 110. The wireless LAN interface card 123 may include at leastone NIC module using a wireless LAN frequency band. For example, thewireless LAN frequency band may be an unlicensed radio band such as theband of 2.4 GHz or 5 GHz.

The memory 130 stores a control program used in the user equipment 100and various resulting data. The control program may include a programrequired for the user equipment 100 to perform wireless communicationwith at least one of the base station 200, the external device, and theserver. The user interface 140 includes various types of input/outputmeans provided in the user equipment 100. The display unit 150 outputsvarious images on a display screen.

Further, the base station 200 according to the exemplary embodiment ofthe present invention may include a processor 210, a communicationmodule 220, and a memory 230.

The processor 210 may execute various commands or programs according tothe present invention and process data in the base station 200. Further,the processor 210 may control all operations of the respective units ofthe base station 200 and control data transmission/reception among theunits. For example, the processor 210 may transmit/process the downlinktransmission signal according to the proposal of the present invention.(See FIGS. 1 to 23.)

The communication module 220 may be an integrated module that performsthe mobile communication using the mobile communication network and thewireless LAN access using the wireless LAN like the communication module120 of the user equipment 100. To this end, the communication module 120may include a plurality of network interface cards such as cellularcommunication interface cards 221 and 222 and a wireless LAN interfacecard 223 in the internal or external type. In the figure, thecommunication module 220 is illustrated as the integrated module, butthe respective network interface cards may be independently disposedaccording to the circuit configuration or the purpose unlike the figure.

The cellular communication interface card 221 transmits/receives theradio signal to/from at least one of the user equipment 100, theexternal device, and the server by using the mobile communicationnetwork and provides the cellular communication service at the firstfrequency band based on a command of the processor 210. The cellularcommunication interface card 221 may include at least one NIC moduleusing the LTE-licensed frequency band. The cellular communicationinterface card 222 transmits/receives the radio signal to/from at leastone of the user equipment 100, the external device, and the server byusing the mobile communication network and provides the cellularcommunication service at the second frequency band based on the commandof the processor 210. The cellular communication interface card 222 mayinclude at least one NIC module using the LTE-unlicensed frequency band.The LTE-unlicensed frequency band may be the band of 2.4 GHz or 5 GHz.

The wireless LAN interface card 223 transmits/receives the radio signalto/from at least one of the user equipment 100, the external device, andthe server through the wireless LAN access and provides the wireless LANservice at the second frequency band based on the command of theprocessor 210. The wireless LAN interface card 223 may include at leastone NIC module using the wireless LAN frequency band. For example, thewireless LAN frequency band may be the unlicensed radio band such as theband of 2.4 GHz or 5 GHz.

In the figure, blocks of the user equipment and the base stationlogically divide and illustrate elements of the device. The elements ofthe device may be mounted as one chip or a plurality of chips accordingto design of the device. Further, some components of the user equipment100, that is to say, the user interface 140 and the display unit 150 maybe selectively provided in the user equipment 100. Further, somecomponents of the base station 200, that is to say, the wireless LANinterface 223, and the like may be selectively provided in the basestation 200. The user interface 140 and the display unit 150 may beadditionally provided in the base station 200 as necessary.

The method and the system of the present invention are described inassociation with the specific embodiments, but some or all of thecomponents and operations of the present invention may be implemented byusing a computer system having a universal hardware architecture.

The description of the present invention is used for illustration andthose skilled in the art will understand that the present invention canbe easily modified to other detailed forms without changing thetechnical spirit or an essential feature thereof. Therefore, theaforementioned exemplary embodiments are all illustrative in allaspectsand are not limited. For example, each component described as asingle type may be implemented to be distributed and similarly,components described to be distributed may also be implemented in acombined form.

The scope of the present invention is represented by the claims to bedescribed below rather than the detailed description, and it is to beinterpreted that the meaning and scope of the claims and all the changesor modified forms derived from the equivalents thereof come within thescope of the present invention.

INDUSTRIAL APPLICABILITY

The present invention is applicable to various communication devicesused in a wireless communication system (e.g., a station using anunlicensed band communication, an access point, or a station using acellular communication, a base station, etc.).

1. A method for a user equipment to receive a downlink signal in a cellular communication system, the method comprising: monitoring a first common control channel indicating a downlink (DL) interval of subframe (SF) #(n−1) and SF #n; monitoring a second common control channel indicating a DL interval of SF #n and SF #(n+1); and performing a DL reception process in the SF #n based on a detection result of the first common control channel and a detection result of the second common control channel, wherein only a detection process for a first physical channel/signal is allowed in the DL reception process in SF #n when a detection of the first common control channel fails, a detection of the second common control channel is successful, and the DL interval of SF #n indicated by the second common control channel is a part of a total orthogonal frequency division multiplexing (OFDM) symbols of SF #n, wherein the first physical channel/signal comprises a Discovery Reference Signal (DRS), wherein the DL interval represents occupied OFDM symbols in a DL subframe.
 2. The method of claim 1, wherein a reception process for a second physical channel/signal is omitted in the DL reception process in SF #n when the detection of the first common control channel fails, the detection of the second common control channel is successful, and the DL interval of SF #n indicated by the second common control channel is a part of the total OFDM symbols of SF #n, wherein the second physical channel/signal does not comprise the DRS.
 3. The method of claim 2, wherein the second physical channel/signal comprises a Physical Downlink Control Channel (PDCCH), an Enhanced PDCCH (EPDCCH), and a Physical Downlink Shared Channel (PDSCH) for downlink transmission.
 4. The method of claim 1, wherein the first physical channel/signal comprises a PDCCH for uplink (UL) transmission.
 5. The method of claim 1, wherein the first common control channel is monitored in SF #(n−1), and the second common control channel is monitored in SF #n.
 6. The method of claim 5, wherein SF #n is comprised in a time window expecting DRS reception.
 7. The method of claim 6, wherein the time window expecting the DRS reception comprises a DRS Measurement Timing configuration (DMTC).
 8. The method of claim 7, wherein the DMTC is configured in a cell of an unlicensed band.
 9. The method of claim 1, wherein the first and the second common control channels comprise a Physical Downlink Control Channel (PDCCH) scrambled with a Cyclic Redundancy Check (CRC) by a Common Control Radio Network Temporary Identifier (CC-RNTI).
 10. A user equipment used in a cellular wireless communication system, the user equipment comprising: a wireless communication module; and a processor, wherein the processor is configured to monitor a first common control channel indicating a downlink (DL) interval of subframe (SF) #(n−1) and SF #n; monitor a second common control channel indicating a DL interval of SF #n and SF #(n+1); and perform a DL reception process in the SF #n based on the detection a result of the first common control channel and a result of the detection of result of second common control channel, wherein only a detection process for a first physical channel/signal is allowed in the DL reception process in SF #n, when the detection of the first common control channel fails, the detection of the second common control channel is successful, and the DL interval of SF #n indicated by the second common control channel is a part of a total orthogonal frequency division multiplexing (OFDM) symbols of SF #n, wherein the first physical channel/signal comprises a Discovery Reference Signal (DRS), wherein the DL interval represents occupied OFDM symbols in a DL subframe.
 11. The user equipment of claim 10, wherein a reception process for a second physical channel/signal is omitted in the DL reception process in SF #n when the detection of the first common control channel fails, the detection of the second common control channel is successful, and the DL interval of SF #n indicated by the second common control channel is a part of the total OFDM symbols of SF #n, wherein the second physical channel/signal does not comprise the DRS.
 12. The user equipment of claim 11, wherein the second physical channel/signal comprises a Physical Downlink Control Channel (PDCCH), an Enhanced PDCCH (EPDCCH), and a Physical Downlink Shared Channel (PDSCH) for downlink transmission.
 13. The user equipment of claim 10, wherein the first physical channel/signal comprises a PDCCH for uplink (UL) transmission.
 14. The user equipment of claim 10, wherein the first common control channel is monitored in SF #(n−1), and the second common control channel is monitored in SF #n.
 15. The user equipment of claim 14, wherein SF #n is comprised in a time window expecting DRS reception.
 16. The user equipment of claim 15, wherein the time window expecting the DRS reception comprises a DRS Measurement Timing configuration (DMTC).
 17. The user equipment of claim 16, wherein the DMTC is configured in a cell of an unlicensed band.
 18. The user equipment of claim 10, wherein the first common control channel and the second common control channel comprise a Physical Downlink Control Channel (PDCCH) scrambled with a Cyclic Redundancy Check (CRC) by a Common Control Radio Network Temporary Identifier (CC-RNTI). 